Optimizer ignores distinct key created for materialized semi-join subquery when searching for best execution plan

create table t0 (a int); 

insert into t0 values (1), (2), (3), (4), (5), (6), (7), (8), (9), (10);

create table t1 (a int);

insert into t1 select (t0.a-1)*10 + (t.a-1) + 1 from t0 t, t0;

create table t2 (a int);

insert into t2 values (12), (88), (47), (33), (28);

select * from t1 where a in (select a from t2 group by a); 

MariaDB [test]> explain extended select * from t1 where a in (select a from t2 group by a);

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

| id   | select_type  | table       | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra                                           |

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

|    1 | PRIMARY      | <subquery2> | ALL  | distinct_key  | NULL | NULL    | NULL |    5 |   100.00 |                                                 |

|    1 | PRIMARY      | t1          | ALL  | NULL          | NULL | NULL    | NULL |  100 |   100.00 | Using where; Using join buffer (flat, BNL join) |

|    2 | MATERIALIZED | t2          | ALL  | NULL          | NULL | NULL    | NULL |    5 |   100.00 |                                                 |

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

3 rows in set, 1 warning (0.00 sec)

MariaDB [test]> show warnings;

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

| Level | Code | Message                                                                                                          |

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

| Note  | 1003 | select `test`.`t1`.`a` AS `a` from `test`.`t1` semi join (`test`.`t2`) where (`test`.`t1`.`a` = `test`.`t2`.`a`) |

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

1 row in set (0.00 sec)

MariaDB [test]> explain extended select * from t1 where a in (select a from t2);

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

| id   | select_type  | table       | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra                                           |

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

|    1 | PRIMARY      | <subquery2> | ALL  | distinct_key  | NULL | NULL    | NULL |    5 |   100.00 |                                                 |

|    1 | PRIMARY      | t1          | ALL  | NULL          | NULL | NULL    | NULL |  100 |   100.00 | Using where; Using join buffer (flat, BNL join) |

|    2 | MATERIALIZED | t2          | ALL  | NULL          | NULL | NULL    | NULL |    5 |   100.00 |                                                 |

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