PO Lines Disappear

Hello,

So we have many problems in our AP department of people stepping back into the lines in the lines tab of a voucher that has been previously matched to a purchase order. When this occurs the PO number disappears from the voucher. This causes a great deal of trouble in our department because the quantity billed can no longer be automatically reversed when the voucher is canceled as there is no longer a PO to tie the transaction back to. At this point we have to have the quantity billed manually reversed and have a new line added to the