Wierd. That update didn't show here until after my posting, and even archive.org did not see it until months after your March announcement. Some bust cache, methinks. No matter! Thanks Florian.
Thirs clarifies the Album Artist situation for me ... to the point where I wonder if %album artist% did every really work as designed!
By the way, assuming by "Winamp" the chart means the current version, Band / Winamp should say "Album Artist" rather than blank.
So, BAND is what mp3tag calls the tag that WMP, iTunes, Winamp, MediaMonkey etc. call Album Artist (officially in WMA and unofficially in ID3). How about mp3tag made things clearer for users by calling it ALBUMARTIST? Retaining BAND for back-compatibility?
Actually, it appears to be the other way around: The starting point is the ID3v2 frame, which is TPE2 according to the chart. The list of declared frames at www.id3.org/id3v2.3.0 indicates that TPE2 is the "Band/orchestra/accompaniment" frame. So mp3tag has stuck with the official name of BAND; the other programs on the chart call it Album Artist.
Regardless of which came first, I've never seen a librarian prog call it BAND, always Album Artist. That's why I think users would be served by Mp3tag doing likewise.