SET STATEMENT slow_query_log has no effect

MariaDB [test]> set global log_output = 'TABLE', global slow_query_log = 1;

Query OK, 0 rows affected (0.00 sec)

MariaDB [test]> set slow_query_log = 1;

Query OK, 0 rows affected (0.00 sec)

MariaDB [test]> truncate table mysql.slow_log;

Query OK, 0 rows affected (0.10 sec)

MariaDB [test]> set long_query_time = 0.000001;

Query OK, 0 rows affected (0.00 sec)

MariaDB [test]> set statement SLOW_QUERY_LOG = 0 for select sleep(0.2);

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

| sleep(0.2) |

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

|          0 |

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

1 row in set (0.30 sec)

MariaDB [test]> select * from mysql.slow_log;

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

| start_time                 | user_host                    | query_time      | lock_time       | rows_sent | rows_examined | db   | last_insert_id | insert_id | server_id | sql_text                                               | thread_id |

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

| 2014-11-02 01:15:20.492680 | root[root] @ localhost [::1] | 00:00:00.000213 | 00:00:00.000000 |         0 |             0 | test |              0 |         0 |         1 | set long_query_time = 0.000001                         |        11 |

| 2014-11-02 01:15:20.798909 | root[root] @ localhost [::1] | 00:00:00.200698 | 00:00:00.000000 |         1 |             0 | test |              0 |         0 |         1 | set statement SLOW_QUERY_LOG = 0 for select sleep(0.2) |        11 |

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

2 rows in set (0.00 sec)