truncation in FETCH reports a wrong row number

SET sql_mode=default;

DROP TABLE IF EXISTS t1;

DROP PROCEDURE IF EXISTS p1;

CREATE TABLE t1 (a INT, b VARCHAR(10));

INSERT INTO t1 VALUES (10,'11x');

INSERT INTO t1 VALUES (10,'12x');

DELIMITER $$

CREATE PROCEDURE p1()

BEGIN

  DECLARE cur1 CURSOR FOR SELECT b FROM t1;

    BEGIN

    DECLARE res int;

    OPEN cur1;

    FETCH cur1 INTO res;

    CLOSE cur1;

  END;

END;

$$

DELIMITER ;

CALL p1();

SHOW WARNINGS;

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

| Level   | Code | Message                                  |

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

| Warning | 1265 | Data truncated for column 'res' at row 3 |

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