Business case :
Purchase Order Has Been Created for Vendor X , Product Line for material Z=10 Quantity
We make a shipments for 10 Quantity .
then we make return of the same shipments for 10 Pieces and we update the check box for Update P.O.
the result will happen that Purchase order Receiving Quantity is 0 that totally correct .
now i want to receive some Quantity on the same purchase order i can't Odoo does not allow me to enter any quantity.
in version 10 there was workaround that just duplicated and enter the shipment
