incomplete files from bitcomet

Today I was downloading stuff with bitcomet and this one file's percentage reached 100%. So I seeded it for a while and did end task with out deleting files. Then I went and checked my downloaddestination folder. It's still marked incomplete. But I try to run it using a program anyways (was .avi file so I could just use windows media player). And it magically worked just fine. 
However, I noticed later that there is this other rar file that is tagged incomplete eventhough this was 100% too. This time I don't know what to do at all. I mean why is bit comet suddenly doing this to me???

have you enabled "rehash when done" ? i had that problem and that fixed it for me.

>>2
thanks you just saved my life