Within the past 24 hours I've seen this occur 6 times either first hand or to members of my group I play with.

What basically happens is in the "Jails" (located primarily near barracks) the walls next to the "Doors that never open" can be accidentally and seemingly randomly clipped through which then traps the player within the walls. While we can see outside of the walls we cannot pass back through them. Twice this has resulted in the death of one of my group other times the player has been eventually able to "jump" back through the wall after a ten minute period of running towards the corners and hitting "v" at the last minute.