CHAR creates different data types in hybrid functions vs UNION

DROP TABLE IF EXISTS t1,t2,t3;

CREATE TABLE t1 (a CHAR(1), b CHAR(2));

CREATE TABLE t2 AS SELECT COALESCE(a,b) AS c FROM t1;

CREATE TABLE t3 AS SELECT a FROM t1 UNION SELECT b FROM t1;

DESC t2;

DESC t3;

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

| Field | Type       | Null | Key | Default | Extra |

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

| c     | varchar(2) | YES  |     | NULL    |       |

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

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

| Field | Type    | Null | Key | Default | Extra |

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

| a     | char(2) | YES  |     | NULL    |       |

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