Incorrect collision behavior against open surfaces
In vanilla-Morrowind, with collision turned ON, the player could walk through the reverse side of non-closed models, the case often being an interior wall piece, a large boulder, or the ceiling of an interior kit piece approached from the wrong side.
This behavior is actually rarely used to create trick walls, or surfaces where the player can go into an area from one direction, but once they pass through the invisible surface of the wall, they cannot return that way because the wall, having been there all along, is now visible from the players point of view, and cannot be passed through again.
Another time when this is helpful is when a player glitches out of the proper play area in an interior and needs to simply get back into the interior from the void. Or when a player COCs to a location and is stuck inside a rock or building model (currently a problem with our coc implementation, since it doesn't take into account statics at the drop-off location).
(RM-806 from redmine: created on 2013-05-31 by Paul McElroy, )