Wrong result for range w/o min endpoint, ORDER BY DESC and ICP

MariaDB [test]> CREATE TABLE t2 (a INT, b INT not null, KEY(b));

Query OK, 0 rows affected (0.038 sec)

MariaDB [test]> INSERT INTO t2 VALUES (2,8),(9,1),(4,6),(11,13),(15,17);

Query OK, 5 rows affected (0.008 sec)

Records: 5  Duplicates: 0  Warnings: 0

MariaDB [test]> SELECT a, b FROM t2 WHERE b != 10 and b < 30 ORDER BY b DESC;

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

| a    | b  |

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

|   15 | 17 |

|   11 | 13 |

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

2 rows in set (0.002 sec)

mysql> CREATE TABLE t2 (a INT, b INT not null, KEY(b));

Query OK, 0 rows affected (0.040 sec)

mysql> INSERT INTO t2 VALUES (2,8),(9,1),(4,6),(11,13),(15,17);

Query OK, 5 rows affected (0.015 sec)

Records: 5  Duplicates: 0  Warnings: 0

mysql> SELECT a, b FROM t2 WHERE b != 10 and b < 30 ORDER BY b DESC;

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

| a    | b  |

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

|   15 | 17 |

|   11 | 13 |

|    2 |  8 |

|    4 |  6 |

|    9 |  1 |

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

5 rows in set (0.002 sec)