INSERT ... ON DUPLICATE KEY UPDATE report the wrong INSERTING/UPDATING/DELETING flag in multi-event triggers

CREATE TABLE t1 (a INT PRIMARY KEY);

CREATE TABLE log1 (msg VARCHAR(20));

--delimiter $

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

BEGIN

  IF INSERTING THEN

    INSERT INTO log1 VALUES ('INSERTING');

  ELSEIF UPDATING THEN

    INSERT INTO log1 VALUES ('UPDATING');

  ELSEIF DELETING THEN

    INSERT INTO log1 VALUES ('DELETING');

  END IF;

END

$

--delimiter ;

INSERT INTO t1 VALUES (1);

# Expected: second log1 row is 'UPDATING'. Actual: 'INSERTING'.

INSERT INTO t1 VALUES (1) ON DUPLICATE KEY UPDATE a = 1;

SELECT * FROM log1;

DROP TABLE t1, log1;

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 log1 (msg VARCHAR(20));

Query OK, 0 rows affected (0.008 sec)

13.1.0-opt>

13.1.0-opt>delimiter $$

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

    -> BEGIN

    ->   IF INSERTING THEN

    ->     INSERT INTO log1 VALUES ('INSERTING');

    ->   ELSEIF UPDATING THEN

    ->     INSERT INTO log1 VALUES ('UPDATING');

    ->   ELSEIF DELETING THEN

    ->     INSERT INTO log1 VALUES ('DELETING');

    ->   END IF;

    -> END

    -> $$

Query OK, 0 rows affected (0.006 sec)

13.1.0-opt>delimiter ;

13.1.0-opt>

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

Query OK, 1 row affected (0.001 sec)

13.1.0-opt>INSERT INTO t1 VALUES (1) ON DUPLICATE KEY UPDATE a = 1;

Query OK, 0 rows affected (0.002 sec)

13.1.0-opt>SELECT * FROM log1;

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

| msg       |

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

| INSERTING |

| INSERTING |

| INSERTING |

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

3 rows in set (0.000 sec)

13.1.0-opt>