When I startup BitComet 0.73, sometimes it cannot auto resume the tasks, even though I have enable to option of "Auto-resume tasks on BitComet startup" in the Preferences - Appearance menu.
I got the similar problem like you after using BitComet 0.71, the file I downloaded was up to 50%+ yesterday and after I shutdown my PC and restarted today, I found the file was reset to about 21%+, it seems to be a bug in BitComet 0.71 !