Unexpected "BIGINT UNSIGNED value is out of range" for minus

DROP TABLE IF EXISTS t1;

CREATE TABLE t1 (

  c1 BIGINT UNSIGNED,

  c2 BIGINT UNSIGNED

);

INSERT INTO t1 VALUES (20030516235329,20000127231341);

SELECT c2-c1 FROM t1;

ERROR 1690 (22003): BIGINT UNSIGNED value is out of range in '(`test`.`t1`.`c2` - `test`.`t1`.`c1`)'

DROP TABLE IF EXISTS t2;

CREATE TABLE t2 AS SELECT c2-c1 FROM t1 LIMIT 0;

SHOW CREATE TABLE t2;

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

| Table | Create Table                                                                                          |

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

| t2    | CREATE TABLE `t2` (

  `c2-c1` bigint(21) unsigned DEFAULT NULL

) ENGINE=InnoDB DEFAULT CHARSET=latin1 |

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