I'm sorry for the unacceptable delay here, I was sidetracked by another project. I just got to test it now, I replaced my fix with yours and the initial problem I had returned.
File fuel/application/core/MY_Model.php
public function initialize, line 112:
if (!empty($params) && is_array($params))
public function form_fields, line ~1764 to 1794:
// create related
if (!empty($related))
{
$key_field = $this->…
correction for first paragraph: ...you will not be able to define a module for the related field ('categories' in the example), and so your model will not load, this might be...