If MERGE option on TABLE and group-by field is computed, it appears the DISTRIBUTE MERGE is generated without the fieldvalue parameter for the MERGE option in DISTRIBUTE and shows as HASH DISTRIBUTE.
DISTRIBUTE(HASH32(_unnamed_1, internal), merge));
versus this when using a discrete field:
DISTRIBUTE(HASH32(fieldvalue, internal), merge*(fieldvalue)*);
The resulting aggregation is incorrect, not consolidated as expected.