[b21] Strange interaction between quake and stairs up

[Frumple]

18:25 Frumple Oh wow
18:25 Frumple Bug, interesting one.
18:26 Frumple If you quake a wall to where a stairs up was, when you come back down stairs, you'll be where the stairs were originally, i.e. inside the wall.

Basically, if you quake-move the stairs up on a level, and a wall lands where the stairs were, when you come back down later, you appear inside the wall and promptly start suffocating.