Finalize voucher when not all po lines are selected

Currently, finalizing a voucher will relieve the po encumbrance during budget check but only for those lines that are associated with the voucher.  What if, for example, you have a 2 line po and are paying off only line 1 but know it is the last payment for the purchase order and want both lines on PO to be finalized.  You would think if you marked finalize at the voucher header level, the entire po would liqudate, at the line level the liquidation would occur at line leve and so on with Distribution level.  This is leaving users uncertain when