I know I once reported it on the ZDForums, and I thought perhaps it would have been perhaps fixed by then, but I can tell the issue still exists in the latest version of MM.
I got a screenshot here from back then in 1.4 of the pillar you can fall behind and get trapped in at the Isle of the Volcano with no means of escape from the position which is located at the north east part of the map to the entrance of the caves with this problematic pillar being beside that small cliff face and the south part of the room.
It was the only softlock I came to when I played it back then, but I plan to play this again with some addons versatile enough to poke fun with, so I might as well try and see if I can find anything else a player might in the mean time.