All possible #music properties should be available on selected items. For a music track/file mp should show all properties (incl. the missing album artist).

Not having the album artist is causing problems on showing cover art (latest music will not show the correct cover if the album artist != artist), you can not show CD art correctly, etc.

For other views (artist/album/etc) MP properties should be available if unique. So if an album only contains one genre, the #music.genre should be filled if the album is selected. If I only have one album for an artist, the #music.album field should be filled. This would allow showing more information to the user.