Wrong result with group by CAST(s AS XMLTYPE);

CREATE TABLE t (s VARCHAR(30));

INSERT INTO t VALUES ('<a/>'),('<b/>'),('<c/>'),('<a/>');

SELECT CAST(s AS XMLTYPE) FROM t;

SELECT * FROM t group by CAST(s AS XMLTYPE);

SELECT count(*) FROM t group by CAST(s AS XMLTYPE);

DROP TABLE t;

MariaDB [test]> SELECT CAST(s AS XMLTYPE) FROM t;

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

| CAST(s AS XMLTYPE) |

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

| <a/>               |

| <b/>               |

| <c/>               |

| <a/>               |

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

4 rows in set (0,002 sec)

MariaDB [test]> SELECT * FROM t group by CAST(s AS XMLTYPE);

+------+

| s    |

+------+

| <a/> |

+------+

1 row in set (0,004 sec)

MariaDB [test]> SELECT count(*) FROM t group by CAST(s AS XMLTYPE);

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

| count(*) |

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

|        4 |

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

1 row in set (0,005 sec)