XOR returns bad results for an indexed column

DROP TABLE IF EXISTS t1;

CREATE TABLE t1 (

  id INTEGER UNSIGNED NOT NULL AUTO_INCREMENT,

   k INTEGER UNSIGNED DEFAULT '0' NOT NULL,

   c CHAR(120) DEFAULT '' NOT NULL,

   pad CHAR(60) DEFAULT '' NOT NULL,

   PRIMARY KEY (id)

) ENGINE=MyISAM;

INSERT INTO t1 (k, c, pad) VALUES (10, 'a', 'xxx');

INSERT INTO t1 (k, c, pad) VALUES (11, 'a', 'xxx');

INSERT INTO t1 (k, c, pad) VALUES (12, 'a', 'xxx');

INSERT INTO t1 (k, c, pad) VALUES (13, 'a', 'xxx');

INSERT INTO t1 (k, c, pad) VALUES (14, 'a', 'xxx');

INSERT INTO t1 (k, c, pad) VALUES (15, 'a', 'xxx');

INSERT INTO t1 (k, c, pad) VALUES (16, 'a', 'xxx');

SELECT * FROM t1 WHERE id XOR 0;

SELECT * FROM t1 IGNORE KEY(PRIMARY) WHERE id XOR 0;

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

| id | k  | c | pad |

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

|  1 | 10 | a | xxx |

|  2 | 11 | a | xxx |

|  3 | 12 | a | xxx |

|  4 | 13 | a | xxx |

|  5 | 14 | a | xxx |

|  6 | 15 | a | xxx |

|  7 | 16 | a | xxx |

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

7 rows in set (0.00 sec)