When you have a data object that contains SimpleXMLElements they can be tricky to access because they look like objects but they aren't accessed in the same way. In this case they appeared to be objects that had the @ symbol in the object name.
For example, a complex object that is used by Form.php $form->xml->fieldset[0]->field[1]->{'@attributes'}['name] but the field elements are actually SimpleXMLElements and not objects.
So, you can view them using:
$form->xml->fieldset[0]->field[1]->attributes()->name;
and write to them using
$form->xml->fieldset[0]->field[$i]['name']