DUPLICATE KEY Errors on SELECT .. GROUP BY that uses temporary and filesort

Import the table provided into a MariaDB 5.5 and/or 10.0 instance, ensure your max_heap_table_size and tmp_table_size are 32M or less, and issue these queries:

SELECT * FROM t_album2 GROUP BY Composer;

SELECT Composer FROM t_album2 GROUP BY Composer;

It returns DUPLICATE KEY errors:
ERROR 1034 (HY000): Duplicate key 1 for record at 583508 against record at 11380

Here is the table structure:

CREATE TABLE `t_album` (

`id_album` int(11) NOT NULL AUTO_INCREMENT,

`Composer` varchar(255) COLLATE utf8_swedish_ci NOT NULL DEFAULT '',

PRIMARY KEY (`id_album`)

) ENGINE=InnoDB AUTO_INCREMENT=1050654 DEFAULT CHARSET=utf8 COLLATE=utf8_swedish_ci;

The GROUP BY must be in the query to trigger the error.

Notice that if I increase max_heap_table_size and tmp_table_size (512M seems to work here), then the query runs as expected.

SET SESSION max_heap_table_size=536870912; 

SET SESSION tmp_table_size=536870912;

After-thought: With the same tmp/heap table sizes, the query runs fine in MySQL 5.5.37, though the bug looks somewhat similar to this open MySQL bug:

http://bugs.mysql.com/bug.php?id=58081