The server should only accept attributes that are valid for the relationship.

Steps to reproduce:

• Turn Javascript off
• Create a relationship, e.g. add a URL to http://test.musicbrainz.org/artist/7e84f845-ac16-41fe-9ff8-df12eb32af55
• Select as many attributes as you like.
• Submit edit

If you turn Javascript off and load http://test.musicbrainz.org/edit/relationship/edit?returnto=http%3A%2F%2Ftest.musicbrainz.org%2Furl%2Fe950e670-7d45-41c3-a842-77789caed361&type1=url&type0=artist&id=331537 you can see that "minor" and "guest" are selected even though the MySpace relationship type doesn't support those attributes.