Known Bugs (Apocalypse)

X-Com Apocalypse - Errors, Oddities, & Strange Behaviour

...also known as "Bugs"

Bugs

Apocalypse bugs listed here are divided (loosely) into two main categories: Cityscape and Battlescape.

When describing any new error:

• explain briefly what happened, or if you don't understand it, what you were doing.
• if you can repeat the bug, describe in concise detail how to make it appear so that others can test it, otherwise it might just be a random glitch.
• explain how or what you did to avoid, or fix, the bug since there may be multiple ways to prevent/fix it.
  
• and if you can, explain your method on how to exploit it.

Extra Information

This may help others work on a solution, but is not necessary to include, and completely optional*:

• what game version (EU or US) of physical CD you used, or
• what digital version (GOG or Steam), or
• if it is some other version available (eg: game magazine CD, free complilation disk etc.).
  

* due to privacy.

What not to include:

• modified (modded) games.
• burned, illegal or pirated games of any sort whatsoever.

Errors, Oddities, & Strange Behaviour

Please Insert CD

A transition from cityscape to battlescape may sometimes bring up this message.
It is an uncommon random occurrance and does not seem to be avoidable (a possible solution is listed below which may work).

To prevent losing your progress in your game, save your game just before you start any mission (base defense mission may start unexpectantly, so save often).

Executables: Old Or New

Digital distributions could be using old versions of certain files whereas better versions would be ideal on modern hardware. An explaination below and an optional fix is listed below.

Cityscape

Start Base: Vehicle Repair Bay Location

The start base may have an incorrectly placed Vehicle Repair Bay as shown:

• 

Restart the game to remove this error.

Cargo Module Capers

This is relevant to the first mission only, and only if the mission is in your starting building. The cargo module will 'remember' briefly what it was carrying (usually brainsucker launchers).
Any vehicle must have a cargo module installed (the Valkyrie at the game start) for this to work and must remain at the base. Agents ready to do battle when an Alien infestation is detected (alert or search, doesn't matter) are selected (not necessary to place them in a vehicle) for battle in the building, do battle as usual, alien infestation is cleared and brainsucker launchers are (should be) recovered (noted in de-brief screen at mission end), seems normal so far.
When checking the sell-agent-equipment screen to find the alien artifacts after mission success, they are not listed. The bug: They have been 'moved' into the cargo module in a vehicle that was not at all involved with this first mission! To properly recover the artifacts, launch the craft which contains the cargo module (the valkyrie?), send it somewhere in the city (the craft must clear the launch tube and leave the base, one cell movement is far enough), then return it to base. A new message appears: "Items from tactical combat zone have arrived: Base 1" ...your brainsucker launchers! (it gets weird now)
The vehicle with the cargo module has got the launchers 'stuck' in it. You can move the module to another vehicle (save the game now to support this explaination) and launch that new craft (as before: the fly-return routine), the message appears now from this vehicle! (Reload that save now). If launching the craft (the valkyrie which had its module removed) by doing the same fly-then-land routine, the valkyrie does not prompt the message... proving that the brainsucker launchers are 'stuck' somewhere in the cargo module and uses zero space!.
To prevent weirdness, pick up a dropped launcher when fighting and store it on the agent. After mission end, remove the launcher and it will disappear (it is an artifact and is now listed in the sell screen). The bio-lab will have a new topic! ...or do the fly-return routine with the craft that has the module. EsTeR

Freeze After Midnight

Sometimes the game might just freeze once it passes a day at 00:00, this freeze is somehow connected to the city repairing itself bit by bit everytime the clock reaches midnight. What exactly causes this is unknown and there are no known ways to prevent this as the city already starts partially destroyed (from the intro cinematic UFO) as well as avoiding city damage during incursions or just by stray Megapol Policecar shots being a nigh impossible thing.
If you encounter a freeze past midnight but have saved the game just before, a way to prevent the freezing (for a while at least) is to destroy more of the city. In this case the Cult of Sirius buildings are a good target, as no matter what you do you will inevitably end up or already start the game with being hostile towards Cult of Sirius. Once you have destroyed some of their buildings, the game should no longer freeze once midnight passes. However, this might have to be repeated everytime a freeze occurs. Sometimes it manages to fully get rid of the freezing, requiring no more destruction of the city, sometimes it can only prevent the freeze for a few days.

Unreliable People Tubes

If many are hired at once, technical personel (scientists and engineers, but not agents) may not be provided a vehicle for transport and are forced to walk to the X-Com base. The bug: If the new technical person is forced to stop moving through a building (no further progress since people-tube is missing), they will remain there and will not move (even with ultra-speed timescale).
To avoid this error, prevent any new hires from being forced to stop at anytime during their foot journey by using ultra-fast time momentarily immediately after hire/fire screen . (Spacebar = pause time).
Agents on foot who are stopped by missing people tubes may be picked up manually by a vehicle.

Ultra-Fast Time Denial: Combat

Cityscape time-scale selection of Ultra-Fast does not work. The bug: Too many vehicles are present or there is an active battle on-going somewhere will prevent "Ultra Fast" time from being chosen.
These is no fix for this except waiting for the time-scale to become valid (press the Ultra-Fast button roughly every second until it activates, spacebar to pause the time)

Ultra-Fast Time Denial: Routing

Cityscape time-scale selection of Ultra-Fast does not work. The bug: A road vehicle is unable to proceed to its destination due to a broken road somewhere which will prevent "Ultra Fast" time from being chosen.
To fix the routing problem it may be necessary to target the vehicle itself for destruction or by collapsing the road section by using Manual Control.

Ultra-Fast Time: Crazy Transportation

If you hire a new unit and road access to your base is not possible or broken, the vehicle may drive around aimlessly. If Ultra-Fast time scale is chosen briefly, the unit is delivered as normal.

Empty Taxi

If an agent/scientist is hired, they may have a road taxi as transport to their destination base. The bug: If the unit is sacked/transfered, the taxi will proceed to the destination base as usual but without the unit on-board. EsTeR

Teleporting Agent(s)

Use the overhead cityscape view. Give an agent a "Go To Building" command. The yellow person icon will start to move to the nearest people tube access point. When the icon is not on the home-cell anymore, but still in the perimeter of your base outline, place that agent into any vehicle and go park/land at a building somewhere. Once at the bullding, go to agent display bar, select that agent and repeat the 'go to building' command given earlier.
The bug: The agent icon will 'teleport' back to the location they were at just before you assigned them to a vehicle. The vehicle parked at a building will be empty! I don't know how this can be exploited. EsTeR

Firing Infatuated Agents

The Hire/Fire screen only displays the first twenty units in their relevant section (agents, biochemists, quantum physicists, engineers) when at a base.
The bug: Others beyond the twenty listed cannot be fired since they do not appear.
To allow others not visibly listed to be fired, they must be transfered to another base (icon only, not physically) so that they appear in the sell/sack screen of this new base with the original base possibly having a reorganised list. (see next bug also: "Sell Agent Transfer Swap").

Automatic Unit-Ratio Reduction

Any unit may be sacked without being chosen if the game decides there are too many units of one type in all your base(s), combined.
The bug: Sacking any unit will also sack another down the list, eg: sacking biochemist #1, will also sack biochemist #21. If more are sacked, the corresponding +1 and +20 unit will be sacked together if the game wants to limit your unit ratios, other types may be fired at random!
The game has an internal limit for how many of a single type of any unit is allowed in regards to the ratio of total X-Com personel. If the game thinks you might have too many units of one type, it will automatically reduce the large differences by selecting random units and adding them to the sell/sack list. Eg: firing one techician might also sack three agents. If many agents are hired in the earlier parts of the game, the game will sack units to reduced the quantity to more manageable levels. Drastic reductions are possible just by opening the Hire/Fire screen, clicking OK, and then you have a message appear of "# units Fired" without actually selecting anyone. To reduced the chance of automatic ratio reductions, don't over populate your bases and be aware of how many you hired or fired as to not be caught out with missing units.
Maximum total of all X-Com personel across all base(s):

Total Limit = 180.

Technical personel of one type = 50.

Agent quantity = 100.

Agent limit if no technical personel employed = 20.

Tested: base quantites, labs present then demolished, selling many at once or just one, increasing ratios tends to trigger this bug and not base quantity or quantity of labs/fabs. Note: This may work in reverse. If many agents are available for hire, closing the sell/sack screen may automatically hire someone (the message appears) if there are too many of that same type in the hire list! EsTeR

Sell Agent Transfer Swap

Transfer units between bases then immediately sell/sack them before they arrive may possibly crash the game.
Typically, if any X-Com unit is transfered to another base, their icon will appear at the destination base (in the sell screen) before they are actually present at their new base.
Eg: Two bases B1 and B2 with agents. Agents at B1 are transfered to B2 and Agents at B2 are transfered to B1 within the same transfer screen. The bug: If these ready-to-transfer agents are immediately sacked then the game very soon may lock up with a black screen or crashes with a page fault. If these transferred units are allowed to arrive at their respective new base then everything seems normal.
Note: This error can persist. If those transferred units are sacked after they have arrived, the game may still crash. To reduced the chance of a random crash: Transfer one group of agents from A to B, press 'OK' to confirm, then transfer second (a different) group of agents from to B to A, again press 'OK', then wait for the transfers to arrive at their destination (use ultra-fast-time if you want), then sack them. If the game crashed for some reason, start game, load your savegame, transfer one group, OK, save, reload that save, transfer second group, save in a different spot, reload this new save, play normally. This may clear out the error from memory (if you crashed with an earlier attempt). Tested: scientists (researching or not), agents (training or not, equiped with something or not, assigned to a craft or not), multiple transfers of the same agents (transfer from A to B, then B to C all in one go) etc... All produced the bug if sold immediately after transfer screen. Used GOG, WinXP-SP3 and a game with many hire/fire uses and at week six. EsTeR

Instant Equipment Transfers On Sacking

If needing to transfer agent equipment immediately, equip an expendable agent(s) with what is needed then transfer them to that base. The bug: The sell/sack screen will display the agent's icon at the new base (but they havn't physically arrived yet) and if that transfered agent(s) is sacked, their equipment will go into the stores of this new base. Exploited easily if any agents are not needed!
Note: This also can be used to 'store' items at a base which does not have a Stores. Any 'equiped' agent transfered to the base (need Living Quarters for this to work) can be sacked and their equipment will remain behind. This also happens when a new base (don't need Living Quarters but an agent is present) is attacked Base Defense and you are successful. The recovered items remain at the base and can be used, transfered as normal! EsTeR

65535 Widget Bug

A massive quantity of a vehicle item may suddenly appear after selling or transferring a dual purpose (air or road) device. The bug: An unresearched exotic item which appears in both "Airbourne" and "Road" vehicle equipment screen may be sold/transferred twice: once in airbourne, then again in road, in the same selll/transfer session and is denoted by -1 quantity.
Negative quantity values of an item is not possible. The game will internally 'wrap' the quantity to the next available positive number which is 65535.
The item usually is unreseached and will take up all storage capacity at the base. If the item is quickly researched, it may be sold for massive profit.
Note: 65535 is 2^16 which is a 16-bit number.

Storage Alchemy

When you sell off all of an alien artifact and it disappears from the sell screen, the game doesn't always re-point your stores correctly. One known possibility is all your Elerium-115 (potentially several hundred) being transmuted into GLM Air Defenses when Cloaking Fields are sold off.

This has been tested has it has nothing to do with alien artifacts or any ammo in particular. This is an error in the update routine when selling off the first item in the list of craft specific items to a zero storage quantity. If you buy a Light Weapons Control the game will give you the correct amount and your list will work as normal. If you happen to sell all the light modules, the quantity amounts (but not item list) of all your items in the Ground Vehicle section (even though you may have sold it in the Air Vehicle section) will be bumped down the list once. The second quantity of the item, that being Medium Weapons Control modules, will be inserted as the third quantity as well! eg: if you have seven medium modules and the repeatable bug appears, then will now have seven heavy modules as well - as long as the technology has been introduced. Repeatable (and exploitable): If you buy all the light modules again (and wait for delivery) and then sell them all, the quantity values will bump down once again! EsTeR

Not to be confused with the 65535 Widget bug which is seperate.

Note: This bug will always appear if the first item in the sell list (in either air or road sell screens) is sold off to a zero quantity.

Ammunition Partial Use

Weapons which have multiple ammo types may be loaded with ammunition which is not displayed in the equip screen. The bug: Partially used ammo is still present in the base and may be loaded into a weapon but all others will be unloaded (when equipping multiple agents at once with the same weapon type). Eg: An autocannon used on a previous mission used an armor-piercing clip (the last remaining one). When back at base, the weapon was removed from the agent and the ammunition (AC-AP) disappeared from the equip-agent screen. In the future, when placing autocannons into multiple agents at once, the first weapon (for the first agent in the list) gets this partially used AC-AP ammunition, but all the other autocannons are empty even with other ammo types available.
When equipping multiple troops, make sure the correct ammo is loaded as well by manually moving the relevant clip onto the weapon icon otherwise some weapons will have no ammunition loaded when starting a mission. EsTeR

Alien Module No Containment

If a base has no alien containment but has a landed craft at the base which contains a bio-module, when aliens are defeated in a base defense mission, the prompt "Keep On Board" or "Destroy" will display. If choosing to 'keep on board' and then moving that craft to another base with an alien containment, no message appears to decide which aliens to keep! The aliens are all killed and corpses are disposed immediately after successful defense of the base! (exactly as expected when no containment is at a base when aliens infiltrate). The bug: Aliens are immediately disposed of and are not placed into the bio-module as expected. EsTeR

Research Lab Topic Swap

Clicking on a lab (but not manufacturing lab) will sometimes swap the active research topic to another which is active in another base regardless if it belongs to that catergory. eg: biology base with four small biology labs and a quantum base with four small quantum labs all researching a topic each. If you click on one of the biology labs, select new topic (without starting the new topic) then press OK, often a quantum topic and research progress will be 'transferred' to this base and the bio topic swapped to the quantum lab. The bug: If a quantum lab was idle, the bio lab new becomes idle and the quant lab is now researching a bio topic! The progress and research continues normally for the swapped topic and thus, can be completed as normal. Obviously this can be exploited by swapping a topic and then starting new research in the lab that got is topic 'stolen'. You could have 4xbio and 4xquan but research seven bio topics. This bug appears always between two bases which have the same layout position of the labs. To make things normal again, click back to the other base and 'start a new project' in the lab which had its topic stolen, - don't select a new topic, just click OK. Things return to how they should be. EsTeR

Is That Base Yours?

Note: This is not a bug! It is listed here to remove confusion about a game process.
Aliens may spread over the city from an initial infestation somewhere by using the people tubes. The Government owns the top-side building which contains an underground X-Com base and as such, the government is susceptable to inflitration just the same as any other organisation (except S.E.L.F). The infiltration/subversion graph may indicate the Government is becoming subverted (an alien alert may appear above your base) and this means that the building above your base(s) needs to searched for aliens as well as any other government owned building.

Rendor Plasma Shot Undercount

The Marsec Rendor Plasma Gun has an inaccurate ammunition capacity listed in the Vehicle Equipment Screen and also in the in-game UFOpaedia. The weapon uses 140 Elerium for a full reload, has 140 shot capacity but has a specification of 70 rounds. The bug: The game divides the ammunition capacity by two for no reason. More information: (http://www.xcomufo.com/forums/index.php?showtopic=242028127). NKF

Battleship "ex nihilo"

An Infiltration Fleet #17 consists of one Battleship (infiltration), one Escort Ship (escort), and a second Battleship (building bombing). This unique fleet has the same UFO-type performing two different missions. The bug: When randomly chosen as a time-tabled mission, the alien dimension only needs one battleship to be present, and not two, for this UFO-group to be valid.
The game internally checks for needed UFOs one at a time. The Battleship once, the Escort once, the Battleship once. The error is that the first battleship 'is found' again. The group will appear in Mega-Primus as normal, but only one Battleship was needed in their homeworld!
Shooting down both battleships will cause the internal count of Battleship-type UFOs present in the alien dimension become -1. The quantity originally was 1xBattleship, but two were used, so the game counter will deduct 2xBattleships! In the following weeks the total will move to positive again and the game will proceed as normal.
Note: "ex nihilo" is Latin for out of nothing something made.

Unlimited Fuel Ghost Engine

Give an air vehicle a "go to location" command away, from your base. When the vehicle is visible in the launch tube, remove the engine back in the "vehicle equippment" screen. The vehicle will fly at the speed at which it exited (about 3) and fly without ever needing to refuel... because it doesn't have an engine!
Hello to Xcom1 and 2 infinite fuel bug!!
but
Giving a command to an engine-less vehicle will cause it to freeze in place, thus, becoming permanently immobile. This can be exploited by being able to have a 'turret in the sky' at your choosing! Use: set attitude to aggressive, height to (preferably) maximum, equip with any lasers (no ammo needed), give it a 'go to location' command, when it is existing the launch tube, remove engine! Do not give it another command until it is in place. Once the craft is in position, give it a new order (eg: "return to base" command). The craft is now frozen in place! You now have a laser turret in the sky! ...doesn't work with road vehicles, however.
The bug: the vehicle moving up the tube is not 'greyed-out' in the vehicle equip screen once 'lifted off', allowing change to be made to the vehicle. This is similar to why multiple-raids-in-quick-succession is possible. EsTeR

Sound: No Interface Or Music

Interface: The interface/battlescape sound may disappear when a battlescape mission has started. Clicking on any button (interface or via keyboard shortcut) is completely silent.
Note: If music is muted as a preference, the battlescape will be completely silent.
Music: The current music has stopped playing/is silent after saving a game or when the battlescape mission ends.
Multiple fixes are possible for either, or both:

• Untick the box for each volume slider within the options screen, then retick each one. Ignore music if not wanted.
• Move each volume slider slightly, then return it to your desired position.
• Wait for the next music track to play.
• Save the game then immediately reload it.
  

and if nothing solves the missing sound/music:

• Quit the game, restart Apocalypse, reload your game.

Sound: UFO Incursion - Battle Music

Note: This is not a bug! It is listed here to remove confusion about a sound process.
Usually you only get an eerie/slightly more worrisome music track playing (Uneasy Calm / The Infestation) during UFO incursions and rarely the battle music (Kill them ALL / Chase) will play.
This is most likely intended design, as the more hype battle music will only play during Apocalypse missions and only if enough UFOs are present. Around 5-6 UFOs minimum are required for the game to play the more threatening sounding tracks. It'll also continue playing as long as enough downed UFOs are still present on the map. Once you recover the wracks and the number of present UFOs on the Cityscape falls below the 5-6 threshold, the music will change back to Uneasy Calm/The Infestation and then back to normal, once all UFOs are recovered/expired.
Due to this, the more hype battle music can and will play regardless of the UFO incursion mission, as long as enough UFOs appear. Though it is most likely meant to only play during the Apocalypse mission.

Wrong Manufacturer

The Dimension Probe and the Anti-Alien Gas Missile for the Marsec Heavy Launcher are incorrectly assigned to Marsec as their manufacturer, when they can in fact only be manufactured by X-COM, and only when the necessary research has been completed. Similarly, given its name and the fact that Marsec doesn't produce other engines, it's likely that the Metro Multipower Plus engine is incorrectly assigned to Marsec instead of General Metro.
This bug has little effect on gameplay, though it will prevent X-COM from (re-)purchasing these items should Marsec turn hostile.

Battlescape

Odd Behaviour

A UFO battlescape shows external weapons on the outside of the crashed craft. Destruction of these weapon systems does not matter in regards to a successful recovery. If any weapon is damaged or completely destroyed, it is recovered at mission completion.

Limits: Items And Units

Battlescape has an item limit of 500 pieces of equipment and a unit limit of 60 entities. The bug: A unit may not appear or those that do appear may have an empty inventory if many X-Com agents (and technical personel when on a Base Defense mission) are used. This may be exploited as a way to stop enemy units being equipped with weaponry or to limit their unit numbers.

500pieces of anything seems to be wrong since I stress-tested an alien spawner and had +700 items within. Pic (bottom of page) EsTeR

Psychotic Agents

An armed agent that has been given a target (RMB on any hostile non-X-Com unit, and not civilians) and then given a Forced-Fire command to shoot something or someone else (but not the RMB target), the agent will not fire on your selected force-fire target, but will shoot at the RMB targeted unit instead ...if it is in line-of-sight ...and will not stop until the target is dead ...until the line of sight to the target is broken!
If the agent is forced to drop the weapon (stop shooting you nutter!), the agent will resume shooting at the RMB target once any weapon is placed back into their hands, if the agent or any other agent, did not break line-of-sight at anytime during these drop weapon actions.
The agent will resume shooting at the RMB target at a new (move) destination... (same paramaters with line-of-sight).
The agent will ignore any further "hold-fire" command (eg: click on aimed shot then quickly back to hold-fire), will ignore changes to attitude (doesn't stop shooting but will perform seeking-cover actions if not aggresive) and will ignore certain movement types (eg: if walking and target is visible = shoot!, if running and at new location and target if visible = shoot!). The bug: the hold fire command is just a suggestion if the RMB target is visible when a force-fire command is given. To cease any more weapon fire from this psychotic agent, break the line of sight (of everyone) momentarily to the RMB-selected target. EsTeR

Boomeroid Bouncer

An armed Boomeroid will 'bounce' on the spot when stuck in the 'grey blobs' of building rubble.
The bug: A boomeroid which is thrown into, or has hopped into, the grey rubble piles found usually at Slum battlescapes will not be able to jump out! The proximity setting works and will explode as expected, but its movement towards a unit is blocked until the grey rubble is destroyed, setting it free to perform as normal until it jumps back into another pile...
A trapped boomeroid will behave like a standard proximity mine if ignored; easily seen bouncing on the spot when it wants to hop!
Note: some map features on any battlescape may block jumping in the same direction. (Dead trees outside of the Graveyard Castle, next to the road). Some may jump 'into' a feature, get blocked, but are able to jump 'out', the same way they came in. Grey blob piles will block boomeroid movement from all directions. EsTeR

Boomeroid Heavy Shadows

An armed Boomeroid will not 'bounce' away if a flying unit's shadow can be seen directly over it, irrelevant how high that unit is above it!
The bug: A Boomeroid which has been armed and thrown, or dropped, and has landed on the ground does not move if any unit's shadow (from a flying unit) is moved and stopped over the device. The shadow prevents the boomeroid from jumping away, thus, making it ignore any movement from anyone.
If an agent attempts to throw a boomeroid into the same cell as the shadow, the throw is denied (even from the adjacent cell).
A "no-jumper" boomeroid will behave like a standard proximity mine and will still obey its arming setting... but never move!
This is a game-breaking bug.
Boomeroids are rendered immobile by shadows... mind blown! EsTeR

Pathway Indecision

A unit may move in an unexpected fashion or is unable to process the best path when given a destination. The bug: Simple routing usually works as normal but complicated paths or dynamically changing routes may confuse an agent by aimlessly moving (and wasting Time-Units in a turn-based game) and may ignore their attitude selection.
Eg: A flying unit given a destination to move into a hole underneath the overhang of a UFO may move towards the roof or try to get inside the UFO by using the external door. To fix such unexpected behaviour, manage their movement in short sections only if a unit seems to be wandering off.

Marsec Armor Mid-Air Death

An airbourne agent is very high up on the battlescape using Marsec armor chest piece. Inventory access will allow removal/re-equip of the chest piece armor which will then cause the agent to 'fall out of the sky' upon returning to the battlescape screen. If the agent's inventory is again accessed before impact, the chest armor may again be momentarily removed and then re-equipped, like normal. The bug: An agent continues falling but will die in mid-air from the first-armor-removal impact (the ground has invisibly 'moved up'), then briefly pauses dead in the air, then will continue falling to the ground.
Each repeat of this 'inventory remove and re-equip' action before the agent has hit the ground will pause the falling, until impact. Height above the ground at which this first armor removal was actioned, will depend if the agent is unaffected, injured, or dead upon impact, however, if there is another agent underneath (typically on the ground) below this flying unit when the armor was manipulated, the falling unit will not be injured when hitting the ground but merely knocked unconscious. This may be exploited by jumping out of a building to escape, disregarding height so long as there is someone to land on. EsTeR

Travelling In Time

Time is irrelevant within a battlescape mission. The bug: A mission may proceed over a long time peroid but returning to the cityscape view shows that the mission only took a few seconds. This can be safely ignored since it does not affect the cityscape time.

Visual Delays

There are some glitches when you move your men flying very high, especially if tall structures are around. You will see "shadows" to appear and move here and there, and, after movement is completed, they will not be cleared until you force a complete redraw of the screen.

Unlimited Flying Stamina

In the turn-based mode when you are flying with the marsec armour at high speed (running) the stamina is unaffected, so that you can run as long as you like and each move has a reduced TUs cost. But if you run out of stamina everything works as if you were walking: the TUs cost of your movements is increased.

Visible Movements

In turn based mode if you spot one or more aliens and you end your turn, the first steps of the alien that moves first (among the ones that you have spotted) are always visible, regardless that the alien is outside of the visual range of any of your men.

Invisible Aliens

Large lifeform's (only Megaspawn or Psymorph) lower body part may not be visible to your agents if their upper body is hidden behind a structure. The bug: The large lifeform may be directly in front of your trooper, but your agent will not see them if the 'head' of the large unit is completely obscured.
Small lifeforms (Hyperworm, Micronoid Aggregate) might not be visible to your agents in certain random situations until the unit moves or your agent is re-positioned (turning on the spot may also help) when it is known that the alien is there. It is common problem with Micronoids.

Personal Cloaking Field Accuracy

The Personal Cloaking Field has an error/hidden property of making the user much less likely to be hit with even the best accuracy weaponry when the user has been spotted/revealed. A hostile may be at point-blank range and being fired upon, but due to having an active cloak effect, the firing unit's accuracy and chance to hit is reduced. To avoid this error in accuracy-calculation, aim at the cell directly behind an enemy target with forced-fire (hold Shift button and LMB to fire) to use the agent's normal accuracy-calculation. This also affects enemy units firing upon revealed X-Com agents.

Ammunition Consolidation

In the agent equipment screen during tactical combat, ammunition can be combined by picking up an ammunition clip and then dropping it onto the same type of clip held in the inventory.
This is not necessarily a bug and likely intended to allow the player to consolidate partial clips such as those used in multi-munition weapons.
What is most likely unintended is that no bounds checking is performed to ensure that the target clip is only refilled to its maximum capacity. Instead the ammunition count for both clips are combined onto the target clip. The held clip on the other hand will be left with a count of 0.
This process can be repeated several times to consolidate multiple clips into a single large clip that only takes up the space of one.
This is a storage space exploit only. The game will still calculate the correct weight of the gestalt ammo clip and weigh down the agent appropriately. A Marsec Heavy Launcher Rocket with a count of 10 for example will still weigh as much as 10 rockets. Brainsucker Pods left with a count of 0 will not hatch.

Android Resistance

By default, Androids are assigned the Human resistance values. Meaning, they will just as quickly fall unconscious to stun damage as Humans and Hybrids, causing Androids to take 100% Stun Gas and 100% Stun (Stun Grapple, Psionics) damage instead of 0% Stun Gas and 20% Stun damage as well as taking 100% Incendiary damage (IN Ammunition, Diablo Incendiary Grenade) instead of only 60%.
Note that this cannot be fixed by using modding programs such as Apoc'd and assigning Androids to the Android Damage Modifier. The reason for this is that Androids are assigned the "X-COM Agents" role, as every soldier is (Humans as well as Hybrids). The "X-COM Agents" role however is assigned the "Human" Damage Modifier Group, which take priority over each individual damage modifier class and therefore overrides the "Android" modifier with the "Human" modifier again. S.E.L.F. units (building security) are treated as humans and will not be affected by this change, either.

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Turn-Based Game Freeze

If you manage to open the inventory screen just as your soldier is dying, the game will freeze.
This can happen in Turn Based mode, if you approach a Popper who starts its reaction turn while your soldier is still walking towards it and you click the inventory button just at that very moment.
When the soldier dies just as the inventory screen is up the entire interface will be corrupted. If you hit the bottom right button, it'll return to the battlescape screen and everything will look normal again, however the game will still act as if you were in the inventory screen.
You will be unable to move your soldiers, shoot, turn, etc. and pressing any of the buttons, even the end turn button, will result in nothing happening. There is no known work-around. If this happens you will have to restart the game.

Security Station Time Units

In turn-based mode, the time units (TU) of the turrets in Security Stations is not refreshed at the beginning of either X-Com's or the aliens' turn. As such, each turret will typically only get one shot off before becoming inert for the rest of the battle (like the aliens, they only start with 25% of maximum TU). This is the reason Security Stations are largely useless in turn-based mode. A guide to fixing this with a hex-editor can be found here.

Brainsuck Near A Door

In turn-based mode when you place a Soldier directly in front of a door, Brainsuckers usually fail to jump on the soldiers head. They usually try several jump attacks until they run out of time units and then end up sitting ducks in front of your soldier with no time units left.
Sometimes though the Brainsucker can get stuck inside the wall above the soldier, remaining invisible for the rest of the mission and preventing it from being completed.
A work around to that would be shooting the wall to destroy it in order to gain visibility of the Brainsucker or having to forfeit and leave the mission with all of your soldiers to proceed or trying to avoid the exploit all together. However, sometimes this is not possible as you might accidentally end your turn in front of a door with a Brainsucker lurking somewhere.
Just keep in mind that if after a failed (not connected) Brainsucker attack the Brainsucker remains gone that it might be stuck inside the wall above the tile it initiated the jump from.

• 
• 
• 

Left picture: Cursor is where your Soldier is positioned before the Brainsucker attack.
Middle picture: Previously invisible bugged Brainsucker revealed after destroying the wall.
Right picture: After ending the turn the Brainsucker regained consciousness but was still unable to move. It visually appeared on level 5 as well, where there was a free walkway, yet the minimap showed its position at the same level as the wall itself.

Brainsucked Toxigun Toxins

Any brainsucked agent is immune to toxigun poisons. The bug: Micronoids take over the human host but do not get killed when an infected agent is shot with toxins.

Aliens Non-Spawn In Large UFOs

Most prominently the Micronoid, being only available through a downed Bomber, fails to spawn on the other bigger UFOs even though it's in the crew list of the UFOs. Making it a very elusive alien to capture before entering the alien dimension, as you'd most likely only get one chance downing the Bomber and catching it alive before you are ready to enter the alien dimension.
This issue happens because of 2 reasons:
1. Aliens are grouped together like your own soldiers, however this can mean that 2-3 troops units can be occupied just by a few aliens, for example: Troop 1 consists of 2 Anthropods, Troop 2 consists of 3 Skeletoids. Even though both troops still have room for more aliens, none of the other alien types are grouped into them. For the bigger UFOs this means, that aliens higher on the spawn list get to be assigned a troop first, and once all troops are occupied, fully or even with only 1 alien, the remaining aliens fail to spawn as they cannot be assigned into those troops.
2. In the Debug and Beta versions of Apocalypse, the game didn't have a limit on how many alien units can be on the map, leading to scenarios where you would have to fight over 40 aliens on the Battlescape, along with more aliens arriving through the map exits or being dropped off and entering the map through the highest available level. The troop/alien number restriction added on the final version of the game makes it impossible for UFOs to spawn more than 36 aliens at once, while on top of that the restrictive troop grouping will prevent the aliens that didn't get assigned to a troop to spawn in the first place. Each organization therefore is hard limited to only 36 possible units, while any human organization other than X-COM, is set to spawn up to a maximum of 20 units only.

Bleeding Impossible To Heal

Sometimes when the Medi-Kit is used to heal Fatal Wounds the wounds will never heal and the Soldier will bleed out. This happens most likely due to the fact that the game once had an "Advanced Medi-Kit" item that would come available after researching Alien Biology. Some Fatal Wounds were meant to be too deadly for the regular Medi-Kit to heal, so the "Advanced Medi-Kit" would have to be used instead.
However, while the "Advanced Medi-Kit" got cut (with many more items and mechanics) before the final release, the deadlier Fatal Wounds were never removed.
The "Advanced Medi-Kit" was meant to come in several iterations (similar to Toxin Type A, B and C), allowing it to not only heal deadlier Fatal Wounds, but also introducing a variant of the current medical screen which would allow the use of various stat boosting chemicals, while also making it usable on other units. On top of that, it was meant to be able to cure brainsucked Soldiers / Human Organisation units (captives in the cut "Cells" base module) after stunning them, allowing you to recover your Soldiers or cure brainsucked Organisation Units for the cut interrogation / spy part of the game.

Base Defense Agent Stripped

A base defense mission which has many X-Com units may leave one agent completely strippped of everything in their inventory. It may go un-noticed since most often technical personel 'suffer' this error and since they do not have an inventory, everything may seem normal. Needs more testing. EsTeR

Battlescape Level 10 Bug

Nine levels is the player-accessible limit for agents to fly high. If an agent who is flying and is on a platform/roof/walkway of some sort at level nine which has a railing (or some other half-height thing) and has been given a move destination, they may fly up (into Level 10) and over this railing-thing to shorten their route. They will immediately come down to level nine and resume their movement. If the unit is ordered to stop (RMB to ignore given orders) when they happen to momentarily be at level ten, they can remain there (normally like any other level). To access this unit to see them at level ten, double LMB on that 'high' agent's portrait picture. The bug: An un-seen height-level with completely normal geometry, features etc. which is not accessible in normal gameplay ...why? EsTeR
Note: To see all ten levels easily of any battlescape, use XME.

Escort Superposition

An Escort UFO battlescape has Stasis Bomb Launchers positioned on the north edge and south edge of the craft in the deployed, ready-to-fire, position. Unconventional access to the floorplan is possible if external weapon systems are destroyed. The bug: If one launcher is damaged (eg: the north one), the other one is immediately destroyed also ...without it sustaining any damage! A 'spooky action at a distance' effect. EsTeR

Cityscape Design

Recyclotorium Two

Superhuman: X-Com is assigned the ownership of Recyclotorium Two, instead of Evonet.
If Warehouse Two contains an X-Com base and is targeted for a Building Bombing mission, the recyclotorium is usually hit along with the warehouse when under attack. Cityscape air battles are slightly less dangerous since damage to the recyclotorium is not damage to the warehouse.

Orphaned Launch Tube

Superhuman: unowned launch tube between Mutant Alliance:Offices and Nutrivend:Offices.

Road Over Tube

Superhuman: road placed over a launch tube of Lifetree:Luxury Apartments.

Unconnected People Tube

Superhuman: unconnected people tube at Government:Lovecraft Block. Does not allow foot movement northwards.

Learning Artificial Intelligence

The Learning Artificial Intelligence (henceforth: "Learning AI") is a feature within X-Com Apocalypse where the game learns how the human player is progressing through the game and will try to implement those tactics into computer-controlled actions dynamically, against the human player. An advanced intelligent learning process! ...which unfortunately does not work, but if it does, is extremely fragile!

Digital Distributions

The Learning AI is dependent on the exact physical location of three files on the original compact disk. Digital distributions such as the Steam or GOG version use
[ .iso] or [ .bin and .cue] image files of the original CD which removes any location data of the three files: EXPERIEN.DAT, BRAIN.DAT, and WEAPEXP.DAT.
The Learning AI files will still update and adjust themselves according to your tactics but will fail to be used in the game due to this missing location data.

Disk Versions With Functional A.I.

Learning AI is active and working on two common UK-based CDs with serial numbers:

• MP191 207 D01R (original UK version)
• PP191 207D01R (a Power-Plus release)

A maximum installation from the orginal CD is preferable, however, a digital distribution which has a customised DOSbox setup pointing to the optical drive and CD within will allow the Learning AI to be active.

Fragile And Broken

• Learning AI will stop working if the game is saved and since a reload needs a savegame, it will be broken.

Please Insert CD Bug

The "Please Insert CD" message may randomly appear with digital distributions of X-Com Apocalypse when the game changes from Cityscape to Battlescape mode. Unless playing with an actual CD in the optical drive, reducing the problem (but not eliminating it) may be possible:
Read through all listed solutions! Don't delete files or folder unless absolutely sure. Copy and Paste everything as a backup before makng changes. USE LEGITIMATE SOFTWARE ONLY.

Solution 1

Digital distributions (Steam or GOG) are using Minimal Installation setups to save space. The game CD is present as an image within the CD folder. Access of this folder may be too slow for the game and may sometimes produce delays which the game interprets as having no CD. To reduce the frequency of the "Please Insert CD" message, manually moving original folders and files will reduce delays of DOSBox of having to search the image. Two methods are possible unless actually installing the game from a CD (which should be "Maximum Installation"):
Install your digital distribution first.
Note: using the following method(s) will automatically make your game a "Maximum Installation".
Method 1
A legitimate CD is needed.

• Copy the contents of the XCOMAPOC or XCOM3 folder on the disk into your already installed digital version. If prompted to OVERWRITE anything select NO TO ALL.

Optional: Delete all PCX files within the UFOPAEDI folder. See: Cargo and Bio-Module since they have swapped pictures. (or manually rename them)

• Check below: "Pentium or DOS Versions"
  

Method 2
A more complex option if an original CD is not available:

• Open an [ .ISO] or [ .BIN and .CUE] file which contains the X-Com Apocalypse game with any compression software (eg: WinZip, 7zip, WinRAR etc.) by RMB and selecting "Open Archive". The contents of the ISO file will become visible.
• See Method 1 to continue.

Note: Don't double-LMB-click the file since it may start your CD burning software. If the .BIN file cannot be opened, burning it to a blank CD may allow finding the needed folder.

Solution 2

Start X-Com Apocalypse through a Virtual Machine (eg: Oracle's VM VirtualBox) which has MS-DOS v6.22 and Windows 95 pre-installed.

Pentium or DOS Versions

If using the downloadable distributions of X-Com Apocalypse, it may be using the old DOS version of two files instead of the better Pentium version. The old version files have been renamed as the better version and this may cause unstable behaviour or introduce bugs.

Files from a dual version (DOS and Windows) X-Com Apocalypse CD.
TACEXE folder:

• TACP4.exe 3,161,594 bytes (DOS)
• TACP.exe 3,170,298 bytes (Pentium)

UFOEXE folder:

• UFO2P4.exe 1,705,790 bytes (DOS)
• UFO2P.exe 1,702,206 bytes (Pentium)

A current discussion about file problems is here:
https://www.gog.com/forum/xcom_series/xcom_apocalypse_serious_distribution_bug_please_fix_gog/page1

A Simple Solution to use the Pentium version:
Note: If copying over the files, BOTH must be the same type. Do not mix a DOS version with a Pentium version.
Check the size (not name) of the files to determine which version has been installed with your digital distribution. If your files match the Pentium size, changes are not needed, however if confirmed they are the old version files:
1. Delete (or cut'n'paste somewhere as a backup) both old version files in your installation. If your install contain four files (two DOS versions and two Pentium versions) remove them all Δ.
2. Copy over from your CD the two Pentium version files to their relevant folders. Renaming them is not needed.
3. Start a new game and go start a raid. If the battlescape loads properly, everything is good. If not, return the original old versions files to their respective folders, overwrite both Pentium versions which failed.
Δ If four files are present: remove any file that does not match the Pentium filesize. Rename only if needed so that X-Com Apocalypse will not use the old versions.

Caution: changing the settings within dosbox_xcomapoc.conf for CPU type from "auto" to "pentium_slow" may decrease performance. Check performance by changing categories within the in-game ufopaedia screens. The animation effect of the menu may have noticable slowness if using pentium_slow.

Defintions Used Here

An explaination of abbreivations or words used within this "Known Bugs" page.

• DOS = Disk Operating System (from Microsoft, eg: MS-DOS).
  

An old pre-windows 16bit program using simple instructions to make a computer useful via a command line interface.

• DOSBox

Emulator software used to run old DOS programs easily within Windows 32bit operating systems often using a temporary (virtual) disk drive.

• EXE = Executable.
  

A suffix on a file allowing it to be started as a program. eg: xcomapoc.exe

• GOG = Good Old Games

A website offering a selection of older games for download at low cost.

• Steam

A website which catalogues certain games purchased by a user to prevent piracy.

• Image

the contents of a compact disk (CD) made into a file(s) (most commonly .ISO) located on the harddrive.

• 486 = a version of computer processing unit (CPU) of a certain format and style.

Very old technology before Intel Pentium processors.

• C:\ D:\ E:\ etc.

Labels given to harddrives using the alphabet, commonly from C to Z with A and B given to floppy-disks drives (another old storage format).

END