UNIQUE key with USING HASH clause changes logic for partitioned tables

MariaDB [test]> CREATE TABLE t1 (a INT, b INT, UNIQUE (b) USING HASH) PARTITION BY KEY (a) PARTITIONS 2;

Query OK, 0 rows affected (0.433 sec)

MariaDB [test]> show create table t1;

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

| Table | Create Table                                                                                                                                                                              |

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

| t1    | CREATE TABLE `t1` (

  `a` int(11) DEFAULT NULL,

  `b` int(11) DEFAULT NULL,

  UNIQUE KEY `b` (`b`) USING HASH

) ENGINE=InnoDB DEFAULT CHARSET=latin1

 PARTITION BY KEY (`a`)

PARTITIONS 2 |

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

MariaDB [test]> CREATE TABLE t1 (a INT, b INT, UNIQUE (b)) PARTITION BY KEY (a) PARTITIONS 2;

ERROR 1503 (HY000): A UNIQUE INDEX must include all columns in the table's partitioning function