Sorry I can't offer much more info than that. I did check the ADOM application directories for error or log files, but there was nothing there. I had to force-quit with task manager. The save file was gone too of course.
In the game, I was pcking up blessed arrows of demon slaying one by one from the floor after slaying a Balor and presumably adding them automatically to my quiver. So I would have been doing comma-space-right arrow, comma-space-right arrow. I was striking the keys fast, so maybe I double-spaced or entered them in the wrong order. I had already cleared out most of the monsters on the level.
Finally, I don't know if this is really a new issue--I've experienced fatal crashes before on D50 or other very crowded levels in v1.1 It's rare, but it does happen.
Too bad, I was looking forward to casting Wish for the first time with that character after saving the world. :-)