Union ALL with wrapped selects -Groub BY -syntax err

A client is having issues with wrapped selects and UNION ALL. I'll attach their original DDL and query, but I have a simplified reproduction case here.

# DDL & Data

create table t2 ( a int, c varchar(50)) engine=columnstore;

insert into t2 values (1, 'CT_PropDelay');

# Query

SELECT * FROM ( select a, c from t2 where c in ('x') group by a, c ) t

UNION ALL

SELECT * FROM ( select a, c from t2 where c in ('CT_PropDelay') group by a, c ) t

• What happens today is an error is thrown:

  ERROR 1815 (HY000): Internal error: IDB-2021: 'c' is not in GROUP BY clause. All non-aggregate columns in the SELECT and ORDER BY clause must be included in the GROUP BY clause.

• The expected outcome is for the query to run - with sample data it would look the same as

  +------+--------------+

  | a | c |

  +------+--------------+

  | 1 | CT_PropDelay |

  +------+--------------+

  1 rows in set (0.080 sec)