I was entering an unknown release of the Grease soundtrack. One track is credited on the CD to "John Travolta, Olivia Newton-John & Cast". It appeared that I could use multi-artist credits to recreate this string: artist John Travolta, joiner ", ", artist Olivia Newton-John, joiner " & ", and an unselected artist with credit text Cast. There was no complaint or red box about the unselected artist. However, I was prompted to create a missing entity (with a very confusing dialog, as the entity had no name), and upon submitting the release, got a MusicBrainz bug screen. I am now unable to go back to the tracklist and remove the credit; I have tried a half-dozen times now, and even though it appears to be gone, I am still prompted for a ghost missing entity. I think I am going to have to re-submit the whole thing.