http://test.musicbrainz.org/recording/a2fb462c-253f-4024-ba47-7ec34cd4f36a/edit : since the artist creditor is not displayed by default you have to click on the artist field to make it appears.

However it triggers an artist lookup on the field artist, and when you ignore it and click on a field of the artist creditor, focus go back to the Artist field and you have click again to your field in the artist creditor.