I have tried a couple times, with edits like http://musicbrainz.org/edit/17646842 to set the alias "Maaya Sakamoto" on http://musicbrainz.org/artist/b6c18308-82c7-4ec1-a42d-e8488bce6618/aliases to be primary for the English locale. Each time the edit appears to have been applied successfully, but the alias isn't updated and still doesn't have the "primary" flag set.