Unexpected error message for CREATE USER when tables are locked

MariaDB [(none)]> create database tdb;

Query OK, 1 row affected (0.001 sec)

MariaDB [(none)]> use tdb;

Database changed

MariaDB [tdb]> create table sample (id integer, description text);

Query OK, 0 rows affected (0.014 sec)

MariaDB [tdb]> create user tdbuser1;

Query OK, 0 rows affected (0.009 sec)

MariaDB [tdb]> lock table sample read;

Query OK, 0 rows affected (0.000 sec)

MariaDB [tdb]> create user tdbuser2;

ERROR 1100 (HY000): Table 'db' was not locked with LOCK TABLES