Repeatable with maria-5.3,maria-5.2,maria-5.1,mysql-5.1. Not repeatable with mysql-5.5

Having a WHERE t3.a IS NULL in a query causes "NULL" to be returned. The same query without the WHERE returns "19".

explain:

explain SELECT t3.a FROM t1 LEFT JOIN (( t2 LEFT JOIN t3 ON t2.a = t3.b ) LEFT JOIN t4 ON t3.a = t4.b) ON t1.a = t2.a WHERE t3.a IS NULL;
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test case:

CREATE TABLE t1 (a int NOT NULL );
INSERT INTO t1 VALUES (9);

CREATE TABLE t2 (a int NOT NULL );
INSERT INTO t2 VALUES (9);

CREATE TABLE t3 (b int, a int NOT NULL);
INSERT INTO t3 VALUES (9,19);

CREATE TABLE t4 (b int) ;

SELECT t3.a FROM t1 LEFT JOIN (( t2 LEFT JOIN t3 ON t2.a = t3.b ) LEFT JOIN t4 ON t3.a = t4.b) ON t1.a = t2.a WHERE t3.a IS NULL;

SELECT t3.a FROM t1 LEFT JOIN (( t2 LEFT JOIN t3 ON t2.a = t3.b ) LEFT JOIN t4 ON t3.a = t4.b) ON t1.a = t2.a;