Do you by chance have the cheat MOO on? I see that you used the wall tool to create the room. With MOO on there might be a situation where the walls don't form a closed room though it looks that way. Try using the room tool instead.
yes, I have moo but it doesn't do anything to the walls and the walls always close for me with or without moo. and it doesn't matter if I used the walls tool or the room tool because the walls are closed. anyways, I fixed that bug by changing some of the graphics settings, like I put the lightning on ultra high and reflections on high and now everythings fine. but that's kinda weird, because I always had my settings on medium and everything was fine until that bug happened.
