Hi qubitoz,
Search files of "Media from FTP", it is dependent on the filter written in the "wp-includes / functions.php".
The 2114 line, please add the ,'xml'.
'code' => array ('css', 'htm', 'html', 'php', 'js', 'xml'),
The 2291 line, please add the following.
'xml' => 'text/xml',