Dropped user's sessions are not killed automatically

--user is logged in and can query tables

MariaDB [mysql]> select count(*) from user;

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

| count(*) |

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

|       25 |

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

1 row in set (0.00 sec)

--user is then dropped by an admin

MariaDB [mysql]> drop user user_to_be_dropped@localhost;

Query OK, 0 rows affected (0.00 sec)

--user can continue querying

MariaDB [mysql]> select count(*) from user;

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

| count(*) |

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

|       24 |

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

1 row in set (0.00 sec)

--Even after flushing privileges

MariaDB [mysql]> flush privileges;

Query OK, 0 rows affected (0.00 sec)

MariaDB [mysql]> select count(*) from user;

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

| count(*) |

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

|       24 |

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

1 row in set (0.00 sec)