The relationship editor remembers the artists entered in a particular release, it's great, it saves time, but in can get crowded when is a release full of artists like http://musicbrainz.org/release/2a87ec40-6f72-48cc-8426-9b685870e815 and the popup menu is all over the widget... (See attached screenshot)
I needed to type a new artist name, and I couldn't see what I was typing, which is kinda bad UI

Maybe the popup menu should always be below the artist name field, and have, like a scrollbar ?