I know that I have seen Zombie AI's have gone through walls but more than a few times as I was looting houses zombies randomly appeared out of rooms I already cleared. (I keep doors closed, paranoid). I don't know if they just spawned there or they saw me through the building and went through the wall/door or what but I think it should be changed so that AI's can only spawn so and so away from the player, not in the next room that you already cleared.