I think whoever designed it needs to release the user guide as to the hierarchy of how the tags are given priority.

At the moment, I've found - via trial and error - that Album Artist seems to have higher priority over Artist. This *is* annoying when you want to see which artist sings the song on a compilation album.

Perhaps it was done this way for searching when you select artist and not to have too many separate entries for <artist> featuring <artists> when you want it filed under just one artist. This seems to be the biggest problem with tagging files. I guess having comma-separated artists won't work - not just because that would be too complex for iPhone users - but for artists such as Earth, Wind & Fire for example.