Cannot create triggers in the database `MYSQL`

I run a MariaDB server with lower-case-table-names=0.

This script returns an error:

CREATE OR REPLACE DATABASE MYSQL;

CREATE OR REPLACE TABLE MYSQL.t1 (a INT);

CREATE TRIGGER MYSQL.tr1 AFTER INSERT ON t1 FOR EACH ROW DELETE FROM t1;

ERROR 1465 (HY000): Triggers can not be created on system tables

This looks wrong, as the database `MYSQL` (with upper case letters) is not system.
Only `mysql` (with lower case letters) is system.