ANALYZE SELECT produces strange r_filtered value on a query with ORDER BY

MariaDB [test]> create table t1 (a int, b int) engine=MyISAM;

Query OK, 0 rows affected (0.24 sec)

MariaDB [test]> insert into t1 values (1,100),(2,200),(3,300),(4,400);

Query OK, 4 rows affected (0.00 sec)

Records: 4  Duplicates: 0  Warnings: 0

MariaDB [test]> analyze select * from t1 where b > 300;

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

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

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

|    1 | SIMPLE      | t1    | ALL  | NULL          | NULL | NULL    | NULL |    4 |      4 |   100.00 |      25.00 | Using where |

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

1 row in set (0.00 sec)

MariaDB [test]> analyze select * from t1 where b > 300 order by b;

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

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

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

|    1 | SIMPLE      | t1    | ALL  | NULL          | NULL | NULL    | NULL |    4 |      1 |   100.00 |     100.00 | Using where; Using filesort |

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

1 row in set (0.00 sec)

MariaDB [test]> insert into t1 select * from t1;

Query OK, 4 rows affected (0.00 sec)

Records: 4  Duplicates: 0  Warnings: 0

...

...

MariaDB [test]> analyze select * from t1 where b > 300;

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

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

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

|    1 | SIMPLE      | t1    | ALL  | NULL          | NULL | NULL    | NULL | 4096 |   4096 |   100.00 |      25.00 | Using where |

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

1 row in set (0.01 sec)

MariaDB [test]> analyze select * from t1 where b > 300 order by b;

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

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

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

|    1 | SIMPLE      | t1    | ALL  | NULL          | NULL | NULL    | NULL | 4096 |   1024 |   100.00 |     100.00 | Using where; Using filesort |

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

1 row in set (0.00 sec)