LP:823169 - Diverging results with GROUP BY + NULL in ANY subquery

The following 2 queries:

SELECT a FROM t1 WHERE b < ANY ( SELECT b FROM t1 GROUP BY b );
SELECT a FROM t1 WHERE b < ANY ( SELECT b FROM t1 );

are equivalent and yet they return identical results. The first query returns no rows, the second returns rows.

Test case:

CREATE TABLE t1 (a int(11), b varchar(1));
INSERT INTO t1 VALUES (NULL,'x'),(8,'d'),(1,'r'),(9,'f'),(4,'y'),(3,'u'),(2,'m'),(NULL,NULL),(2,'o'),(NULL,'w'),(6,'m'),(7,'q'),(2,NULL),(5,'d'),(7,'g'),(6,'x'),(6,'f'),(2,'p'),(9,'j'),(6,'c');

SELECT a FROM t1 WHERE b < ANY ( SELECT b FROM t1 GROUP BY b );
SELECT a FROM t1 WHERE b < ANY ( SELECT b FROM t1 );

Repeatable in maria-5.3,maria-5.2, mysql-5.5