I may have discovered a bug in Mp3tag (v2.39) regarding the handling of composer tags when a CD is ripped by Windows Media Player 11.
This is only an issue for songs that have more than one composer, such as almost any Beatles CD (where most of the songs are credited to John Lennon and Paul McCartney). For example, if the Abbey Road CD is ripped (to WMA Lossless) by WMP11, 14 of the 17 songs have "John Lennon; Paul McCartney" in the WMP Composer column (as determined from AMG, the other 3 being credited to George or Ringo). And if I examine the tags in some other tool (such as the dBpoweramp Explorer extension (v12.3), the Composer is also shown to be "John Lennon; Paul McCartney". But if I view the ripped songs in Mp3tag, the Composer column contains only one name for each of those 14 songs: "John Lennon". However, if I highlight any of them and go to View -> Extended Tags..., what I see is:
ALBUM = Abbey Road
ARTIST = The Beatles
BAND = The Beatles
COMPOSER = John Lennon
COMPOSER = Paul McCartney
GENRE = Rock
PROVIDER = AMG
Note the two COMPOSER tags. If I edit any of the other tags in the main window (even if I make no change), the name in the Composer column changes to "Paul McCartney" and if I then go back to View -> Extended Tags..., I find that the "COMPOSER = John Lennon" tag has been removed (permanently). I can, of course, re-edit the tag in the main window to say "John Lennon; Paul McCartney" and this sort of fixes things (the Extended Tags dialog now shows the tag as "COMPOSER = John Lennon; Paul McCartney", which is not quite the same as there being two COMPOSER tags), but that's a royal pain to have to do for every track that has multiple composers, especially when it's not obvious in Mp3tag which tracks do.
This is also a problem for tracks ripped (to FLAC) with dBpoweramp CD ripper (v12.3), which similarly stores multiple composers in multiple COMPOSER tags.
Have I missed an important configuration option, or is this really a bug?
(I can include screen shots if you need them.)