I have an issue with MM4 where some albums are missing from artists as seperate album entries on the Artist menu, or if they do appear, some of them are missing tracks. However, the album appears if you select the artist name itself and look in the library window. Apologies, it's very hard to actually explain!
If I highlight the tracks through the library window though and check the "Album Artist" tag, it then appears under the artist's drop list. Thinking the Album Artist was different, I checked each file individually for another artist it was occuring with, but the Album Artist entry was the same.
Is MM4 not applying the Album Artist entry correctly or something when it auto-fills it? This wasn't an issue at all with MM3