Reordering/adjusting line items on saved invoice after fulfillment

An interesting situation occurred today. We put through a sales order, moved it through fulfillment (including generating some backordered items) and generated an invoice.

The customer sent a PO based on the quote and we wanted to structure the items (and sub-totaling) on the invoice to reflect the way the customer's PO was sub-totaled which was different from how the quote/sales order was structured.

I thought we could simply edit the invoice and use the "move up" "move down" buttons normally seen on lists but there was none. So we proceeded to add the same item in a new position on the list, sub-total appropriately and then delete the same item from its old position in the list. This ended up causing problems with backordered counts as the new item did not pick up the backordered count and deleting the old removed the backordered count.