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).
#3 Updated by Paul McElroy over 4 years ago
I asked around. Haplo, the administrator of Tamriel-Rebuilt, the largest ongoing modification for Morrowind, tells me that TR uses this functionality. His exact words:
Yes, we do use this feature multiple times. The most memorable time is in an ayleid ruin interior cave by Hemitheon in an as-of-yet unreleased part of the map. It was probably an oversight in vanilla Morrowind that let this happen (it probably wasn't intended to work that way, or at least not to be used), but since it exists, I know we at TR and probably other mods have used it too. -Haplo
#6 Updated by Paul McElroy over 1 year ago
This bug has been referenced recently:
It seems other mods use the "one-way collision" behavior present in Vanilla, however the commenter (NatalieN) in the post through the link suggested that old mods need to and can be updated to avoid making use of it to make them compatible with OpenMW.