Phantom Music Videos appear when audio files added, can't get rid of them - Help!

I added some audio plays to my Music Library, labelled in the normal way. During the first import I had four episodes the were in .mov containers (they were .m4a’s that had been edited using quicktime, to cut out unwanted sections, which then saved them as .mov). I realised my mistake, removed the file, rescanned the library and added converted mp3 versions back and scanned again. This issue occurred with one episode in one play and three in the second play.

If I remove both plays and re-index, the phantom Music Videos disappear. When I add back either of the problematic plays and re-scan, then all four “Music Videos” appear. If I click any of them the error is “Playback error Please check that the files exist and the necessary drive is attached”

The information seems to be cashed somehow. Is there anyway of clearing these phantom videos out?

I am running the Plex Server on a Synology NAS and viewing using the web interface on OSX.
I do not have any Music Videos on the server.

Thanks,