Wrong result (extra rows and wrong values) with incremental BNLH

CREATE TABLE t1 (a int) ENGINE=MyISAM;

INSERT INTO t1 VALUES (1),(2);

CREATE TABLE t2 (b int, c int) ENGINE=MyISAM;

INSERT INTO t2 VALUES  (1,2),(3,4);

CREATE TABLE t3 (d int, KEY(d)) ENGINE=MyISAM;

ALTER TABLE t3 DISABLE KEYS;

INSERT INTO t3 VALUES  (5),(6);

ALTER TABLE t3 ENABLE KEYS;

CREATE TABLE t4 (e int primary key) ENGINE=MyISAM;

INSERT INTO t4 VALUES (1),(2);

SET SESSION join_cache_level=2;

SELECT * FROM t1 LEFT JOIN ( ( t2 LEFT JOIN t3 ON c = d ) JOIN t4 ) ON b = e WHERE e IS NULL;

SET SESSION join_cache_level=4;

SELECT * FROM t1 LEFT JOIN ( ( t2 LEFT JOIN t3 ON c = d ) JOIN t4 ) ON b = e WHERE e IS NULL;

SELECT * FROM t1 LEFT JOIN ( ( t2 LEFT JOIN t3 ON c = d ) JOIN t4 ) ON b = e WHERE e IS NULL;

a	b	c	d	e

SET SESSION join_cache_level=4;

SELECT * FROM t1 LEFT JOIN ( ( t2 LEFT JOIN t3 ON c = d ) JOIN t4 ) ON b = e WHERE e IS NULL;

a	b	c	d	e

1	NULL	NULL	NULL	NULL

2	NULL	NULL	NULL	NULL

SELECT * FROM t1 LEFT JOIN ( ( t2 LEFT JOIN t3 ON c = d ) JOIN t4 ) ON b = e;

a	b	c	d	e

1	1	2	NULL	1

2	1	2	NULL	1

EXPLAIN EXTENDED

SELECT * FROM t1 LEFT JOIN ( ( t2 LEFT JOIN t3 ON c = d ) JOIN t4 ) ON b = e WHERE e IS NULL;

id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra

1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	

1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where; Using join buffer (flat, BNL join)

1	SIMPLE	t3	hash_index	d	#hash#d:d	5:5	test.t2.c	2	50.00	Using where; Using index; Using join buffer (incremental, BNLH join)

1	SIMPLE	t4	hash_index	PRIMARY	#hash#PRIMARY:PRIMARY	4:4	test.t2.b	2	50.00	Using where; Using index; Not exists; Using join buffer (incremental, BNLH join)

Warnings:

Note	1003	select `test`.`t1`.`a` AS `a`,`test`.`t2`.`b` AS `b`,`test`.`t2`.`c` AS `c`,`test`.`t3`.`d` AS `d`,`test`.`t4`.`e` AS `e` from `test`.`t1` left join (`test`.`t2` left join `test`.`t3` on(`test`.`t3`.`d` = `test`.`t2`.`c` and `test`.`t2`.`c` is not null) join `test`.`t4`) on(`test`.`t4`.`e` = `test`.`t2`.`b` and `test`.`t2`.`b` is not null) where `test`.`t4`.`e` is null