extra warning "Unknown error" after update with invalid xmltype

MariaDB [test]>   CREATE TABLE t (x XMLTYPE);

Query OK, 0 rows affected (0,032 sec)

MariaDB [test]> INSERT INTO t VALUES ('<a/>'),('<b>1</b>'),('<n>4.5</n>'),('<c/>');

Query OK, 4 rows affected (0,016 sec)

Records: 4  Duplicates: 0  Warnings: 0

MariaDB [test]> UPDATE t SET x = 'xxx';

ERROR 1525 (HY000): Incorrect XMLTYPE value: 'xxx'

MariaDB [test]> show warnings;

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

| Level | Code | Message                        |

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

| Error | 1525 | Incorrect XMLTYPE value: 'xxx' |

| Error | 1105 | Unknown error                  |

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

2 rows in set (0,001 sec)