When merging a constituent record, the spouse does not appear to be added on the target ID. The relationship appears to get merged successfully but the spouse does not get added which results in error in name formats and at times households. Specifically, when there's an existing spouse relationship with the both the target and source with only the primary spouse on the source, it will not make that primary spouse on the target record after merge.
We're currently evaluating this issue for a fix in a future release.
Steps to Duplicate
1. Create 2 records with the same spouse relationship. 2. Make the target record not have a primary spouse relationship. 3. Make the Source record have a primary spouse relationship with the same constituent record for spouse as step #2. 4. Go to Constituents > Duplicates > Merge 2 constituents. 5. Enter your Target and Source and click Merge. Notice the primary spouse relationship is not populated.