I was going to run out of room on my normal download disk, so I wanted to move one of my very large downloads to a new disk. I know that in uTorrent, I had to stop a torrent before I could move the location, and it disables the File Location right-click option if the torrent is running. I saw that qBittorrent would allow me to change the File Location while the torrent was running, so it appeared the qBittorrent was smarter than uTorrent and would handle the move by itself, while the torrent was running.
Alas, this was not the case. The torrent started downloading new pieces to the new location, and the old pieces remained in the old location. So the torrent was now messed up.
My suggestion is to disable the File Location right-click option while the torrent is running, like uTorrent does. This would help prevent the corruption that I experienced.