WTF?

Okay, so I grabbed a torrent of a Queen show (Chicago '78).  That was a while ago.  I removed the torrent itself from my BT client and kept the files themselves...or so I thought.  Somehow, all but "Tie Your Mother Down" disappeared.  I finally found the torrent again, downloaded all the files (took forever due to a lack of seeders), and seeded for a week or two.  I remove the torrent again, being very careful to make sure I kept the downloaded files, and the thing deletes the mp3s.  It's only done that with this one torrent.