I breached the door by casting knock. The room was a mixed tension room in the lower left corner of the level. I still "feel a certain tension" every so often whilst on the level, despite having cleared the room. Possibly related, there was a threat room also on this level (the room to the east of the tension room, with the candy in the doorway) full of Harpies.

Happened on the server. I think he's running Ubuntu 64 bit.

edit: I also read a scroll of magic mapping to make sure that I hadn't missed something.