When currency code is defined at the supplier level, does it retain that currency code through vouch

If you default a currency code in by supplier and use that on a requisition and purchase order, what should happen when the PO is vouchered?   Should the currency code on the voucher be the same as what is on the PO or does the voucher pick up the currency code from the bank.  We would like it to retain what is on the PO from the supplier even if the bank is different.