I've seen in the FAQ the link to flactag, but I'm still a bit
confused. Is it possible to set this up as a plugin so I can edit tags
directly from Rhythmbox or do I need to do it all from outside? I also
don't understand why some of the songs I converted to FLAC have good
tags and others don't.
Not to completely circumvent your question (I don't have an answer), but I use MusicBrainz Picard for my tagging, since it skips all the manual importing and works really well (unless your music collection is really obscure).
Let me know off-list if you want any help with it; I'd be happy to show you its strengths and such.
Cheers,
Andrew