Implicit cast from INET6 UNSIGNED works differently on UPDATE vs ALTER

SET sql_mode='';

CREATE OR REPLACE TABLE t1 (a INET6, b INT UNSIGNED);

INSERT INTO t1 VALUES (NULL, 0x61);

UPDATE t1 SET a=b;

SHOW WARNINGS;

SELECT * FROM t1;

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

| Level   | Code | Message                                                         |

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

| Warning | 1292 | Incorrect inet6 value: '97' for column `test`.`t1`.`a` at row 1 |

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

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

| a    | b    |

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

| ::   |   97 |

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

SET sql_mode='';

CREATE OR REPLACE TABLE t1 (a INT UNSIGNED);

INSERT INTO t1 VALUES (0x61);

ALTER TABLE t1 MODIFY a INET6;

SHOW WARNINGS;

SELECT * FROM t1;

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

| Level   | Code | Message                                                         |

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

| Warning | 1292 | Incorrect inet6 value: '97' for column `test`.`t1`.`a` at row 1 |

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

+------+

| a    |

+------+

| NULL |

+------+