I complied a list of all of these long ago on the Relic News forum, but over time they became outdated or incorrect for one reason or another.
Here's all the bugs I've encountered in The Last Stand (some of these are likely to be present in the rest of the game)
I'll probably make multiple posts to separate Hero bugs from the arena bugs.
(Arena based bugs)
1. Walk-through gate glitches - I wont go into much detail here as it has been a well known issue for a long time, and there's even another thread about it on here. But basically, on some gates a unit can jump/warp onto a specific section of the gate just as it starts to close. This then allows the unit in question to be able to walk through further impassible terrain and thus leave the arena. This happens on the West gate of the Blooded Colosseum and the East gate of the Anvil of Khorne map.
2. Getting stuck gate glitches - On the Anvil of Khorne map, a player with the warp / teleport ability can warp into the gates as they start to close. Depending on the section of the gate, the player wont be relocated next to the gate but instead be inside one of the segments and become stuck. However, the player can still warp back out but while sitting in there, they become "un-reachable" to enemy melee units.
3. Gates obstruction fire - On the Blooded Colosseum map, the gates can obstruct certain ranged weapons - this itself is fine, BUT the gates still obstruct these weapon even when they have fully opened, causing the ranged weapons to hit "nothing" and just disappear without a collision explosion or sound. The prime examples of these weapons are the Mekboy's Rokkit Launcher and the Terminator Captain's Cyclone Missile Launcher. In addition to that, the Tau's Fragmentation Missile Barrage always hits the gate even though the missiles' trajectory have them flying over the gate in all cases.
4. Unreachable playing areas - On the Blooded Colosseum map, there are 2 areas where a player can jump/warp to but aren't directly connected to the main playing arena, preventing enemy units from being able to reach a player who has decided to exploit these areas. The obvious one is an area between the south and west gate (closer to the west gate) which starts off blocked by some rubble. However, if this rubble is removed, then any player can jump/warp to. Typically you'll see Tau players spawning their Drone into this location as the Drone automatically destroys the rubble when it is spawned. The other is in the right corner of the north gate. Although this offers less protection than the other exploitable area, it still prevents enemy melee units from reaching you, as well as being blocked from harm by units inside the north gate area.
5. Not relocating on wave 20 - On both maps, players (and their minions) will sometimes fail to be relocated to the gate areas as the cut scene appears. It looks as if actions like "jumping" right before the cut scene can further encourage this bug (it looks like that the game gets stuck repeatedly trying to relocate that player and eventually runs out of time - and not getting round to the other players). Also the Chaos Sorceror is NEVER relocated. The effects for doing so take place, but the Sorceror is left put.
6. Loss of abilities when dying exiting/entering a building - when entering or exiting a building, your Hero's abilities are temporarily disabled. However, if your Hero were to die during this point, then the abilities remain disabled when your Hero is revived. However, players can fix this by simply re-entering and re-exiting a building. But of course, if there aren't any buildings standing anymore, then you can't do anything about it and stuck with no abilities for the remainder of the game!
7. Floating in mid air - it appears that if a player was to leave a building the very second it is destroyed, the player wont be killed and will exit the building. However, the player will exit the building at the same height they were in the building, resulting in them being able to walk in mid-air. This renders them immune to melee attacks and grounded abilities.
8. The Swamlord is not The Swarmlord! - Killing The Swarmlord counts as killing only a single Termagant, awarding only the points for such a unit, as well as displaying the termagant name.
9. The Seer Council of Banshees! - Each Warlock in the Seer Council is considered to be a Banshee for the purpose of kills, awarding only the points of a Banshee and displaying their name.
10. Shuriken platforms all round! - The Eldar Guardians that accompany the Shuriken platforms also count as being Shuriken platforms for the purpose of kills, awarding more points than they should, as well as displaying the Shuriken platform name upon their death.
11. Loss of AI - Occasionally, the AI for enemy units "stops working" and the unit is left standing around doing nothing till a player comes within very close proximity. In some cases you can get close enough to them to shoot them but not close enough to "re-activate" them, allowing you to just sit there and shoot them to death while they don't do anything in return.
12. AI no use abilities? - On the Anvil of Khorne map, there are some units that wont use their abilities, but can do so in the Blooded Colosseum map or when cloned by the Sorceror. These units are Space Marine Scouts not using their Stealth and Frag Grenades, Assault Cannon Dreadnought not using its sweeping fire attack and Blood Letters not using their Warp ability.
13. Spinning Deffdread - Ork Deff Dreads seems to be able to rotate their body 360 degrees and will perform this with very "twitchy" animation. I.E: the body could be facing one direction then suddenly rotate at blinding speed to face the complete opposite direction.
14. Dead enemy commanders still target-able - Fallen doppelgangers and enemy commanders (such as the Lictor Alpha and Warboss) can still be targeted by abilities and interrupt the players' cursor's actions. This means that while trying to cast an ability on an enemy unit that is standing on top of a fallen enemy command, you are likely to actually cast the ability on the fallen enemy commander instead - wasting the ability. Further more, this can even obstruct reviving an allied fallen commander as the enemy commander will obstruct your reviving cursor.
15. Wrong music? - On wave 20 of the Blooded Colosseum, the game used to play a Chaos theme back before Retribution came along. But since then, it now plays a random casual / un-themed music track.