NEW.col IS NULL disagrees with NEW.col's actual value in multi-event triggers

CREATE TABLE t1 (a INT PRIMARY KEY);

CREATE TABLE log2 (is_null_flag VARCHAR(5), new_val INT, old_val INT);

--delimiter $$

CREATE TRIGGER trg BEFORE UPDATE OR DELETE ON t1 FOR EACH ROW

BEGIN

  IF DELETING THEN

    INSERT INTO log2 VALUES (IF(NEW.a IS NULL, 'YES', 'NO'), NEW.a, OLD.a);

  END IF;

END

$$

--delimiter ;

INSERT INTO t1 VALUES (1);

DELETE FROM t1 WHERE a = 1;

# Expected: ('YES', NULL) -- NEW has no meaning for DELETE.

# Actual: ('NO', NULL) -- is_null_flag disagrees with val in the same row.

SELECT * FROM log2;

#clean up

DROP TABLE t1, log2;

13.1.0-opt>CREATE TABLE t1 (a INT PRIMARY KEY);

Query OK, 0 rows affected (0.009 sec)

13.1.0-opt>CREATE TABLE log2 (is_null_flag VARCHAR(5), new_val INT, old_val INT);

Query OK, 0 rows affected (0.007 sec)

13.1.0-opt>

13.1.0-opt>delimiter $$

13.1.0-opt>CREATE TRIGGER trg BEFORE UPDATE OR DELETE ON t1 FOR EACH ROW

    -> BEGIN

    ->   IF DELETING THEN

    ->     INSERT INTO log2 VALUES (IF(NEW.a IS NULL, 'YES', 'NO'), NEW.a, OLD.a);

    ->   END IF;

    -> END

    -> $$

Query OK, 0 rows affected (0.005 sec)

13.1.0-opt>delimiter ;

13.1.0-opt>

13.1.0-opt>INSERT INTO t1 VALUES (1);

Query OK, 1 row affected (0.002 sec)

13.1.0-opt>DELETE FROM t1 WHERE a = 1;

Query OK, 1 row affected (0.001 sec)

13.1.0-opt>

13.1.0-opt>SELECT * FROM log2;

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

| is_null_flag | new_val | old_val |

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

| NO           |    NULL |       1 |

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

1 row in set (0.000 sec)

13.1.0-opt>

13.1.0-opt>DROP TABLE t1, log2;

Query OK, 0 rows affected (0.009 sec)

13.1.0-opt>