See attached screenshot. Editing http://test.musicbrainz.org/release/cc1bdf41-e28d-4db7-89d2-69bc2392322a/edit I attempted to add a new artist and change the release artist to it. Also added a barcode but dont think relevant.
Note that in the displayed diff, "Eason Chan" is not displayed as the new artist in "Edit Release" - it's empty.
Agreed to leave fix within 3 months by the scheduling game and http://chatlogs.musicbrainz.org/musicbrainz-devel/2012/2012-02/2012-02-09.html