Hi,
this piece of code seems useless:

--- FieldEditor.php.orig 2007-01-19 12:01:24.000000000 +1300
+++ FieldEditor.php 2007-06-11 11:35:20.000000000 +1200
@@ -114,16 +114,6 @@
}*/

function addfield() {
- // get the last field in this form editor
- $parentID = $this->form->getRecord()->ID;
- $lastField = DataObject::get('EditableFormField', "`ParentID`='$parentID'", "`Sort` DESC", null, 1 );
-
- $nextSort = 1;
-
- // the new sort value is the value of the last sort + 1 if a field exists
- if( $lastField )
- $nextSort += $lastField->Sort;
-
$className = "Editable" . ucfirst($_REQUEST['Type']);
$name = $this->name;
if(is_subclass_of($className, "EditableFormField")) {

maybe it's not useless, maybe there should be something like

$e->Sort = $nextSort;

later in the code

I think you are right there. It looks like the line to update the sort of the new element is missing.

The default ordering would display the fields in the expected order.