When two entities that can have relationship credits are merged and relationship credits haven't been chosen for renaming, the name of the old entity is added as a credit for any relationships it had that had no credit already, in order to save the name: https://github.com/metabrainz/musicbrainz-server/blob/9942e134f71df5b0c34ab7f020e498fdb5ea2df8/lib/MusicBrainz/Server/Data/Relationship.pm#L545-L558
This makes sense in most cases, but it does not make sense for the merge of two entities of the same name (but with different disambiguation or whatever). In that case, we end up with a relationship with a credit that already matches the merged entity name. As such, it just looks a bit dumb and is not required at all to save the name, which is the only reason we're doing this to begin with. We should probably make sure the name is different before we save it.
I had to remove some manually today:
I don’t undesratnd why… maybe the relationships were added while https://musicbrainz.org/edit/49295603 was pending?
But AC should still have been cleaned up.