The various behaviors, unless my test environment is tainted:
A) iTunes Client talking to iTunes Server: All extra metadata in Playlist URL entries saved in iTunes Playlists are hidden in normal “eyeball button” library Browse and the “search” box. (This is the exact same behavior when using iTunes locally.) The Playlist URL entries never appear outside of the Playlist itself; the “Library” doesn’t see it.
B) iTunes Client talking to Firefly svn-1301: All extra metadata in Playlist URL entries are visible in normal “eyeball button” browse and the “search” box. Genre entries are the biggest offender, since the other fields are normally blank unless you’ve set them yourself. The Playlist URL entries appear in the normal library.
C) SoundBridge to iTunes Server: Equivalent of B.
D) SoundBridge to Firefly svn-1301 (thanks to your hack fix): Equivalent of A.
Make sense? “B” is the concern.