UPDATE IGNORE does not produce warnings upon duplicate key

create table t1 (a int unique);

insert into t1 values (1),(2),(3);

update ignore t1 set a = 4;

# Cleanup

drop table t1;

MariaDB [test]> update ignore t1 set a = 4;

Query OK, 1 row affected (0.008 sec)

Rows matched: 3  Changed: 1  Warnings: 0

MariaDB [test]> select * from t1;

+------+

| a    |

+------+

|    2 |

|    3 |

|    4 |

+------+

3 rows in set (0.001 sec)