Different UNSIGNED flag of out user variable for YEAR parameter for direct vs prepared CALL

DROP PROCEDURE IF EXISTS p1;

DROP TABLE IF EXISTS t1;

CREATE PROCEDURE p1(OUT v YEAR) SET v = 2010;

CALL p1(@a);

PREPARE stmt FROM 'CALL p1(?)';

EXECUTE stmt USING @b;

DEALLOCATE PREPARE stmt;

CREATE TABLE t1 AS SELECT @a AS a, @b AS b;

SHOW CREATE TABLE t1;

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

| Table | Create Table                                                                                                                     |

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

| t1    | CREATE TABLE `t1` (

  `a` bigint(20) unsigned DEFAULT NULL,

  `b` bigint(20) DEFAULT NULL

) ENGINE=InnoDB DEFAULT CHARSET=latin1 |

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