I was runnig into a house that have some stairs, but my character traspassed the door, note that it was closed, and I was underground of this house, and zombies trasspassed too. I got stucked for a while then went back from where I entered and it worked... The zombies didn't make it :'(

Another thing is that when running inside a building with various floors, on the third one my character went sort of "flying" and then I was inside a wall... Inside a Wall!! I couldn't move, nor traspass it with the "V" command, I could't even look around with my mouse, my character started to sort of gliding on the air and went down slowly, after like 3 minutes my character reached the ground and then I was able to move and trasspassed the wall, no harm was made to my character.

Well, I hope I can help you with the game :)