Genre/Subgenre Bug

When I make a genre a subgenre of a genre that doesn't contain songs,
the genre disappears, the new top level genre created never appears and
the artist seems to be lost track of in the database, even though you
can't reimport the songs.
 
Example:
 
I wanted to create a top level genre "Rock" which wouldn't contain
songs, but just sub-genres.  To attempt this I edited the genre "Indie
Rock" and made it a subgenre by checking that subgenre of box and then
typing in Rock.  Now, any artists in that genre don't show up anywhere,
even in the list artists window.
 
Any suggestions?
 
Josh Thornes