I have deleted a few torrents after they showed little or no seeding.
So when I looked to see about this, I noticed that other torrents that completed and automatically moved on completion to my 'finished' folder, left behind empty folders in my incoming folder.
Maybe this failure to do a full cleanup is related to what you experienced. I am using win7 pro also.
I also note that over the last many weeks, the devteam has been busy re-writing lots of the core functions of tixati and specifically with file handling. Perhaps this will fix this behavior or if not, maybe they will add it to the list of bug fixes needed during the next round of beta testing which will begin very soon.
http://testing.tixati.com/