CAST(date_sp_variable AS TIME) returns a wrong result

mysql> SELECT CAST(DATE'2001-01-01' AS TIME);

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

| CAST(DATE'2001-01-01' AS TIME) |

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

| 00:00:00                       |

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

1 row in set (0.00 sec)

mysql> DROP PROCEDURE IF EXISTS p1;

Query OK, 0 rows affected (0.02 sec)

mysql> DELIMITER |;

mysql> create procedure p1()

    -> begin

    ->   declare t date;

    ->   set t=date'2001-01-01';

    ->   select cast(t as time);

    -> end|;

Query OK, 0 rows affected (0.04 sec)

mysql> CALL p1|;

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

| cast(t as time) |

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

| 00:20:01        |

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

1 row in set (0.00 sec)

Query OK, 0 rows affected, 1 warning (0.00 sec)