The current code in AuthoritiesMarc.pm rewrites all subfields from the report tag in the authority record to fields in related bibliographic records when merging authorities. Additional subfields in the biblio records (e.g. relator code or term) are lost in the process.
The patch retains the original algorithm but restores the additional subfields from the original biblio record when rewriting the linked marc fields.
The problem also exists in 3.0. Two separate patches have been submitted.