Wrong result for a query with [NOT] IN subquery predicate if the left part of the predicate is explicit NULL

Let's create and populate tables t1 and subq with the following commands:

CREATE TABLE t1 (pk INT NOT NULL, i INT);
INSERT INTO t1 VALUES (0,NULL), (1,NULL), (2,NULL), (3,NULL);
CREATE TABLE t2 (pk INT NOT NULL, i INT NOT NULL, PRIMARY KEY(i,pk));
INSERT INTO t2 VALUES (0,0), (1,1), (2,2), (3,3);

Then the query
SELECT * FROM t1 WHERE NULL NOT IN (SELECT i FROM t2 WHERE t2.pk = t1.pk)
is expected to return an empty set.

However in MariaDB 5.1/5.2/5.3/5.5 we have:

MariaDB [test]> SELECT * FROM t1 WHERE NULL NOT IN (SELECT i FROM t2 WHERE t2.pk = t1.pk);
+----+------+
| pk | i |
+----+------+
| 1 | NULL |
| 2 | NULL |
| 3 | NULL |
+----+------+

We also have wrong results for the query
SELECT * FROM t1 WHERE NULL IN (SELECT i FROM t2 WHERE t2.pk = t1.pk) IS UNKNOWN:

MariaDB [test]> SELECT * FROM t1 WHERE NULL IN (SELECT i FROM t2 WHERE t2.pk = t1.pk) IS UNKNOWN;
+----+------+
| pk | i |
+----+------+
| 0 | NULL |
+----+------+

This bug supposedly is fixed mysql-5.6 (see http://bugs.mysql.com/bug.php?id=58628)