If you use the release tracklist advanced editor, you can type in an artist name but not select an artist from the dynamic dropdown. If you do this, no artist is linked, but the fields are still filled in.
In this state, you are still able to submit the edit with the unlinked artist.
Naturally the rest of the site isn't very happy, and you get errors like this:
http://test.musicbrainz.org/user/kepstin/open-edits