With NGS,many group artists are no longer necessary, and should be replaced with the individual artists if they exist only to represent a short term collaboration (right)? However, the new website has trouble handling this case.

E.g. see this recording http://musicbrainz.org/recording/8a6d34d3-5ddf-4b61-858b-c3f0b3ff2c1b with Linda Ronstadt and Johnny Cash. To "fix" it, I need to edit the recording, and I expand Artist, Add Artist "Linda Ronstadt", Add Artist "Johnny Cash" and finally Delete Artist "Linda Ronstadt and Johnny Cash".

If I follow this sequence, though, the website returns an error when I "Enter Edits":

Artist credit field is required

I've removed one artist credit, but left two others in its place. What's wrong?