This one comes from a game played on a Windows 7 (64-bit) laptop.
The only circumstance I know in this case was that I had just lost another character to errant barrel explosions (caused by a former human shot, it looks like), going from 52% to dead in the course of one action. When trying to go to the mortem screen, this popped up:
An unhandled exception occurred at $004C1F6B
EAccessViolation : Access violation
$004C1F6B TBEINGAI__SCAN, line 227 of doomai.pas
$004C077B TBEINGAI__RUN, line 38 of doomai.pas
$004AAc95 TBEING__ACTION, line 622 of dfbeing.pas
$0041B146 TDOOM__RUN, line 409 of doombase.pas
$004020B7 main, line 92 of doomrl.pas
The saved mortem file also says I died to a lost soul, but take a look at the graveyard screen from the mortem:
###########################################################
./....#.......#..../....#.......#....+....#.......#....####
.#....#.......#..0.#....#.......#....#....#.......#....####
.#..../......./....#..../......./....#....+.......+.;..####
/#....#.......#....#....#.......#....#....#########...}####
./....#.......#...>/....#.......=....+....+.......+====####
#####/####/####/#######/####+====X#######+####+####+#===###
./.......#.#......./...%...=.====..../.......#.#.....=0==##
.#....%%.#.#.......#.....===.====....#.......#.#.##########
.#.....%.#.#.......#........=====....#...|.;.+.+.#ssO.0####
.#/#######/#######/#....%....#s|s....#########+#.#ss...####
.+.......%...B...../.........#h.s...0/.........#.+sss..####
#==##.####/####/#######+####/####.#######+####+####+#######
==.........#.......+.......#.#.......+.......#.#.......####
.#=#######+#.......#^......#.#.#######.......#.#.##########
.#......./......0..#...^...+.+.#h....#..}....+.+.#.....####
.#...0...#.#.......#########+#.#.....#########+#.#.....####
./...0...#.#.......+.........#.+.....+.........#.+.....####
###########################################################
###########################################################
The only lost souls I see are well out of melee range, so I'm guessing the mortem bugged out when trying to determine what actually killed me, but I don't know.
If there's anything else I need to say, go ahead and let me know. I still have the mortem file and my notes from this playthrough.