Agree with the explanation and if you think about it, the problem lies in the OS : For not *hard* deleting the file when you shift-delete it. Windows media player is not smart enough to figure out that the missing pieces are part of an old file. Utorrent isn't programmed to delete the space clean before it pre-allocates the torrent files because it may take few seconds to do that and the fear that the user might think utorrent is slow.