Duplicates created when editing in Subject Headings authority file

[jenniferward]

If a Subject Heading is merged through the Subject Headings authority file, a duplicate 650 can potentially be created in the source record. Example: https://muscat.rism.info/admin/sources/1001037282/edit had both Volkslied and Folk songs. Volkslied was presumably merged with Folk songs, and now the Sources record has Folk songs (as a result of the merge) and Folk songs (from the original record). Should there be a check when merging to avoid duplicates in Sources?