I guess the reason it worked was due to some kind of a failure within the client caused by the game freeze when these buttons were pressed simultaneously. The game thinks your character is moving, and for some reason forgets some movement restricting limitations for a short gap in time? Any way, it wasn't like you could walk through anything. Or then it could also be some issue with the coordinates and character location. Perhaps the game teleports/rubberbands/rollbacks the character to invalid coordinates and makes it possible to walk up the walls in BDW.
I don't really know. I'm no developer :P