Wrong result for MAX(COALESCE(time_column))

DROP TABLE IF EXISTS t1;

CREATE TABLE t1 (a TIME);

INSERT INTO t1 VALUES ('10:20:30'),('10:20:30');

SELECT MAX(a), MAX(COALESCE(a)) FROM t1;

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

| MAX(a)   | MAX(COALESCE(a)) |

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

| 10:20:30 | 7594:20:30       |

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