I have several Paul McCartney albums in my music collection. Each track is tagged with the correct name (via musicbrainz, but visually checked as well), and nfo file lists the artist as Paul McCartney.
Under metatdata manager, the artist is just listed as paul. Editing it in the manager and even locking it, after scan it displays the artist as paul again.
This is more of a cosmetic thing to me, because when I search for mccartney, it finds the albums/tracks, so it's just the way it's displayed