Do both of these "members" exist on the Source/versioning side of Integrity then? You're not talking about an Integrity item to source member relationship? It almost sounds like a " source link field " relationship, but as far as I remember that only exists between Integrity item, and a Source member. Not two Source members.
You may want to open up a Support case to ask about this. Hopefully, one of the Integrity support engineers can chime in here if they see it.