Dynamic SQL must be rejected with ERROR 1336 when using non-safe context

CREATE OR REPLACE TABLE t1(a INT);

DELIMITER $$;

CREATE OR REPLACE FUNCTION f_leaf() RETURNS INT

BEGIN

  EXECUTE IMMEDIATE 'INSERT INTO t1 VALUES (777)'; RETURN 1;

END

$$

CREATE OR REPLACE FUNCTION f_mid() RETURNS INT

BEGIN

  DECLARE x INT;

  SET x = 100 + f_leaf(); RETURN x;

END

$$

CREATE OR REPLACE PROCEDURE p()

BEGIN

  DECLARE r INT DEFAULT f_mid();

END

$$

DELIMITER ;$$

CALL p();

SELECT * FROM t1;

13.1.0-dbg>CREATE OR REPLACE TABLE t1(a INT);

Query OK, 0 rows affected (0.028 sec)

13.1.0-dbg>DELIMITER $$

13.1.0-dbg>CREATE OR REPLACE FUNCTION f_leaf() RETURNS INT

    -> BEGIN

    ->   EXECUTE IMMEDIATE 'INSERT INTO t1 VALUES (777)'; RETURN 1;

    -> END

    -> $$

Query OK, 0 rows affected (0.004 sec)

13.1.0-dbg>CREATE OR REPLACE FUNCTION f_mid() RETURNS INT

    -> BEGIN

    ->   DECLARE x INT;

    ->   SET x = 100 + f_leaf(); RETURN x;

    -> END

    -> $$

Query OK, 0 rows affected (0.008 sec)

13.1.0-dbg>CREATE OR REPLACE PROCEDURE p()

    -> BEGIN

    ->   DECLARE r INT DEFAULT f_mid();

    -> END

    -> $$

Query OK, 0 rows affected (0.010 sec)

13.1.0-dbg>DELIMITER ;

13.1.0-dbg>

13.1.0-dbg>

13.1.0-dbg>call p();

Query OK, 1 row affected (0.007 sec)

13.1.0-dbg>SELECT * FROM t1;

+------+

| a    |

+------+

|  777 |

+------+

1 row in set (0.001 sec)

13.1.0-dbg>