Strange savefile incident

[Ycombinator]

I was playing the game, left it in the locked session, session crashed, game process was killed. I restarted the game when I returned, and found @ on the stairs on the same level. Ok, this is expected behavior, game is saved when you enter new level. I played more, made chardump and quit. It was clvl 15. Now I start Angband... and my character is lvl 7, @ is in the middle of level, no stairs nearby. It picked up much earlier version, but how? Even if game was closed incorrectly last time (but I'm pretty much sure I quit via Ctrl+X), savefile must have been rewritten numerous times when I entered new levels. lvl 15 dump remains there at ~/.angband/Angband.
There must be reasonable explanation, but I can't come up with one.

Linux x86-64, trunk r1971