JooDB sorts the values in the groupselect fields alphabetically ascending
function getColumnVals in the catalog model
$query = "SELECT count(distinct(`".$this->_joobase->fid."`)) AS count,a.`".$column."` AS value, '' AS delimeter FROM `".$this->_joobase->table."` AS a ".$cw." GROUP BY a.`".$column."` ORDER BY a.`".$column."` ASC";
$values = $this->_getList($query);
But you want the SET-List from your column.
If you replace these two lines by the following statement it should do the trick.
if (!empty($type[1])) {
$values = (!empty($type[1])) ? preg_split("/,/",str_replace(array(")","'"),"",$type[1])) : null;
} else {
$query = "SELECT count(distinct(`".$this->_joobase->fid."`)) AS count,a.`".$column."` AS value, '' AS delimeter FROM `"
.$this->_joobase->table."` AS a ".$cw." GROUP BY a.`".$column."` ORDER BY a.`".$column."` ASC";
$values = $this->_getList($query);
}