Currently if yo are in the large iron military bunker/house (at the bases and camps) on the top floor if you lay prone and aim down your characters body will end up below the floor and you (or AI) are able to shoot through the floor and basically kill anyone on the lower floor.
I was just playing with some AI and walked in the building seeing the torso and head of an AI unit aiming and shooting at me through the ceiling. {F18132} {F18133}
See pic.
On a side note. This bunker/house als has troubles with the floors when you try to crawl inside. The floor makes you stand up at certain spots (close to the enterance for example).
The same goes for the lower floors. With some of those buildings you're able to crawl under and change your stance, the result is you can peak inside and shoot or throw grenades.
I can't reproduce peeking down through the roof, but peeking up through the floor from beneath the structure is always reproducable by me. No need to change your stance either, simply angle your aim upwards through the floor and your character will clip through allowing you to fire into the building.
Likewise, when crawling under the building, the 3rd person camera clips through the floor allowing one to see inside. See: http://www.youtube.com/watch?v=11ZaikSE50M#t=1m30s. Grenades can also be thrown through these floors: http://feedback.arma3.com/view.php?id=3171. And another related ticket: http://feedback.arma3.com/view.php?id=2521.
The clipping through the roof/ceiling I only have seen AI do that so far because they lock on to you like a robot and keeps pointing his weapon at you when you enter that building. It can be reproduced by placing an opfor AI on the roof in stealth/danger mode and then make sure he has detected you and then walk in the building.
I was just practicing some close quarters room clearing with a buddy of mine and he got shot twice through the roof. We enter, clear the first floor, hold at the stairs, and then we hear a plethora of automatic gunfire, only for me to look down at my buddy dead on the ground with arms or a gun poking through the ceiling.
Issue closed as obsolete. If you encounter this problem again, please create another ticket. Thank you.