Cannot Create Backorder for Amount Only PO

I am not able to create a backorder for a PO which is marked as Amount Only.  I receive the message, 'No rows selected for processing. (10205,103),' when I attempt to select Apply Backorder & Save.

This particular PO is in Dispatched/Valid status and has a Partial Receipt Status.  Each line has an Order Amount of 1500 with 640 Amount Received and 860 as Open Amount.  The Invoice shows that only 480 has been invoiced each line leaving the Un-invoiced Amount as 1020 for each line.

My question is how do I do a backorder for this PO the amount remaining.  I am attaching Excel file, 'Cannot_backorder_for_AmtOnly_PO.