ZEROFILL on a stored function return type is not applied to the function's own result

CREATE TABLE t_zf (c INT(5) ZEROFILL);

INSERT INTO t_zf VALUES (7);

SELECT c, CONCAT(c), CAST(c AS CHAR) FROM t_zf;

CREATE FUNCTION f_zf() RETURNS INT(5) ZEROFILL DETERMINISTIC RETURN 7;

SELECT f_zf(), CONCAT(f_zf()), CAST(f_zf() AS CHAR);

CREATE VIEW v_zf AS SELECT f_zf() AS c;

SELECT c FROM v_zf;

CREATE TABLE t_zf3 AS SELECT f_zf() AS c;

SHOW CREATE TABLE t_zf3;

10.11.19-opt>CREATE TABLE t_zf (c INT(5) ZEROFILL);

Query OK, 0 rows affected (0.010 sec)

10.11.19-opt>INSERT INTO t_zf VALUES (7);

Query OK, 1 row affected (0.001 sec)

10.11.19-opt>SELECT c, CONCAT(c), CAST(c AS CHAR) FROM t_zf;

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

| c     | CONCAT(c) | CAST(c AS CHAR) |

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

| 00007 | 00007     | 00007           |

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

1 row in set (0.000 sec)

10.11.19-opt>CREATE FUNCTION f_zf() RETURNS INT(5) ZEROFILL DETERMINISTIC RETURN 7;

Query OK, 0 rows affected (0.002 sec)

10.11.19-opt>SELECT f_zf(), CONCAT(f_zf()), CAST(f_zf() AS CHAR);

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

| f_zf() | CONCAT(f_zf()) | CAST(f_zf() AS CHAR) |

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

|      7 | 00007          | 00007                |

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

1 row in set (0.000 sec)

10.11.19-opt>CREATE VIEW v_zf AS SELECT f_zf() AS c;

Query OK, 0 rows affected (0.003 sec)

10.11.19-opt>SELECT c FROM v_zf;

+-------+

| c     |

+-------+

| 00007 |

+-------+

1 row in set (0.000 sec)

10.11.19-opt>CREATE TABLE t_zf3 AS SELECT f_zf() AS c;

Query OK, 1 row affected (0.005 sec)

Records: 1  Duplicates: 0  Warnings: 0

10.11.19-opt>SHOW CREATE TABLE t_zf3;

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

| Table | Create Table                                                                                                                        |

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

| t_zf3 | CREATE TABLE `t_zf3` (

  `c` int(5) unsigned zerofill DEFAULT NULL

) ENGINE=InnoDB DEFAULT CHARSET=latin1 COLLATE=latin1_swedish_ci |

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

1 row in set (0.000 sec)

10.11.19-opt>