[BH] Some rooms don't have outline/don't allow room type assignment

As soon as the fence next to my staircase met the wall, the room was no longer public and not assignable. But if I draw all but the last piece of fence, then draw 1 tile of fence in the middle of the room and pick it up and move it to where I want it, the room stays public.

(The first time this bugged, I had to entirely delete and redraw the room to get the outline back - possibly because I had left build mode then gone back in before deleting the fence? - but the second time just hitting undo brought it back. Neither time did I bother restarting.)