Hi Juan,
I realise this is an old post but I had the same problem and hopefully this will help someone else.
I changed the SQL statement on line 89 of SubmittedFormReportField.php from
$tmp = DB::query("SELECT DISTINCT `Name`, `Title` FROM `SubmittedFormField` LEFT JOIN `SubmittedForm` ON `SubmittedForm`.`ID` = `SubmittedFormField`.`ParentID` WHERE `SubmittedFormField`.`ParentID` IN (" . implode(',', $inClause) . ") ORDER BY `SubmittedFormField`.`ID`")
to
$tmp = DB::query("SELECT DISTINCT `Name` , `Title` FROM ( (SELECT `Name` , `Title` FROM `SubmittedFormField` LEFT JOIN `SubmittedForm` ON `SubmittedForm`.`ID` = `SubmittedFormField`.`ParentID` IN (" . implode(',', $inClause) . ") ORDER BY `SubmittedFormField`.`ID`) AS `tmp` )")
It basically forces the ordering to happen before the table is reduced with the distinct command - apparently DISTINCT and ORDER BY don't work well together.