I get this in XBMC
XBMC needs the Album Artist tag to be set right.
I've checked that it appears to be set correctly in MP3Tag.
However it doesn't work as expected, so I tried to determine what the problem was, and in Foobar2000 I found the answer.
How do I get MP3Tag to set the actual "Album Artist" field and not an extra field that XBMC (or anything else) would ignore?