I don't understand either. I see this more frequently lately, that (informative, on topic) posts are randomly killed. It's not like the poster was a negative-karma user, either. Who decides which posts get killed?

Often it's because a user accidentally double-posts, the second post gets auto-killed, the user can't see their own dead posts, and they delete the live one rather than the dead one (because they can't tell which is which).

bbatsell hit this correctly. I saw two replies appear and immediately killed one. It surprises me to see replies on the dead one, there were no replies when I did the kill.

Clearly, to keep the balance in the system, if there is auto-kill, there must be auto-unkill also :D