Add support to the AutoComplete widget for binding ID of selected item to the value of the record being edited.  At the you can only bind the text-field.  This is useless for related records.
It's not good for much if you can't bind the id of the selected record, like in the Combo.
It should also have an option to only allow matching records.  So if the user types something that doesn't match it won't bind... and validation can pick up a null value that way....