Can't seem to remove non-existent Genres from music library

Hello all- New to XBMC and loving it so far. Running on a G-Box midnight. When I update my music file genres using MP3Tag (getting rid of odd genres from 1st library import to XBMC), these no-longer-existing genres are remaining in the music library Genre menu. clicking on one of them in the music library leads to an empty view with no associated track. I have triple confirmed the genres do not exist in my library on any tracks, and I have done a 'clean library' and 'update library' several times. Any idea how I can fix this without removing / reimporting the entire source library? Seems like newly added genres show up ok, but old ones previously listed in XBMC and now removed from media files do not go away.

TIA-

XBMC Frodo 12.0 - Confluence