This may not be a bug in MP3tag, but something isn't right somewhere.
I used MP3 tag to change the album tag of ~800 MP3s. The vast majority work correctly on both my MP3 player and in xmplay, but there's a few which display the old album tag in xmplay, and a few which show "unknown album" on my MP3 player - and the tracks at issue are different on my MP3 player and in xmplay!
With the unprintable bytes filtered out, the tag section from one of those which is wrong in xmplay is:
Track01TitleJubei's ThemeAlbumNinja Scroll TV OSTArtistVariousAPETAGEXTAGJubei's ThemeNinja Scroll TVBest of Anime OST vol 52003allall & wWw.***.Ru
I note that "Best of Anime OST vol 5" is my new album tag, whilst "Ninja Scroll TV OST" is the old album tag - both are present?
Meanwhile the filtered bytes of the tag from one which appears with no title on my MP3 player is:
TAGGetawayBoogiepop Phantom - Susumu YokBest of Anime OST vol 5allall & wWw.***.Ru
Any ideas what is up?