When people merge releases that have different works on both sides, we end up with one MB Recording that is a recording of both MB Work A and MB Work B. MB Work A and MB Work B are duplicates that need to be merged.
When people merge releases that have the same works on both sides, but different attributes, we end up with one MB Recording that is both a recording of MB Work A and a cover recording of MB Work A. One of the recording relationships need to be deleted.