Funny, there are several people who "reproduce" the bug in differnt ways.
On my third game, I saved after killing some constructs and azo. After killing Azo, I sneaked upstairs without any fight. No one was hostile. I reloaded, attacked a construct which hit a guard(I think this was the trigger for the people upstairs going hostile), killed the construct, went upstairs and everyone was hostile.
Oh and I avoided the central room.