Lost soul clipping problems

"Block monsters" flag circumvented
Lost souls created by a dying pain elemental may occasionally be hurled through a monster-blocking linedef (type 1) if their initial angle is nearly perpendicular to that line.

Trapped outside level boundary
When a pain elemental is destroyed near a wall (one-sided linedef), it may eject one or more lost souls through the wall, who then become trapped outside the map (not in a sector). Such lost souls cannot normally be killed, and although they do not affect the player's kill percentage, their action sound may help to conceal other demons who make the same sound.

A lost soul outside the level can still open a door, if the appropriate linedef is between it and the player (and sufficiently close to the map boundary).