DESC attribute upon spatial index creation prevents ER_DUP_INDEX warning

CREATE TABLE t1 (c POINT NOT NULL);

ALTER TABLE t1 ADD SPATIAL INDEX b1(c DESC);

ALTER TABLE t1 ADD SPATIAL INDEX b2(c DESC);

# Cleanup

DROP TABLE t1;

MariaDB [test]> ALTER TABLE t1 ADD SPATIAL INDEX b1(c DESC);

Query OK, 0 rows affected (0.024 sec)              

Records: 0  Duplicates: 0  Warnings: 0

MariaDB [test]> ALTER TABLE t1 ADD SPATIAL INDEX b2(c DESC);

Query OK, 0 rows affected (0.026 sec)              

Records: 0  Duplicates: 0  Warnings: 0

MariaDB [test]> ALTER TABLE t1 ADD SPATIAL INDEX b1(c);

Query OK, 0 rows affected (0.023 sec)              

Records: 0  Duplicates: 0  Warnings: 0

MariaDB [test]> ALTER TABLE t1 ADD SPATIAL INDEX b2(c);

Query OK, 0 rows affected, 1 warning (0.024 sec)   

Records: 0  Duplicates: 0  Warnings: 1

MariaDB [test]> show warnings;

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

| Level | Code | Message                                                                             |

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

| Note  | 1831 | Duplicate index `b2`. This is deprecated and will be disallowed in a future release |

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

1 row in set (0.000 sec)