Redshift Spectrum error with DATE type partition column on JSON table

I am receiving the "DATE data type can be used only with text, Parquet, or ORC data files, or as partition column." for queries on a JSON-based external table:

Interestingly, I can SELECT it in case it is not wrapped in aggregate:

The table is defined with below partition clause and works as expected when querying via Athena, but produces above error when accessed via external schema in Redshift Spectrum.

Is this a bug or a error in the documentation? CREATE EXTERNAL TABLE doc specifically mentions that DATE data type is allowed as partition column just as the error message I receive when running aggregate on the partition column. Swapping DATE to CHAR(10) works, but I'd rather use correct data-type... This is on Redshift v1.0.49780

Thanks, Alex