Apparent incorrect validation of GROUP BY fields when ONLY_FULL_GROUP_BY sql_mode enabled

After executing set session sql_mode = 'ONLY_FULL_GROUP_BY', running the attached query (query.sql) in the database created by attached database.sql gives "SQL Error (1463): Non-grouping field 'BENEFIT_INDICATOR' is used in HAVING clause", even though the verbatim BENEFIT_INDICATOR field is included in the GROUP BY.

Related, but not so much a bug, I had to include additional fields in the GROUP BY compared to other DBMS to get it to run without the HAVING clause - the validation appears to have issues field names included in the CONCATs in the GROUP BY.