Work Confirmation Receipts

Hi,

We have an approved work confirmation.  In rcv_shipment_lines, the approval status of all lines is APPROVED and the amount_received sums to $17,200.  In rcv_transactions, the receive & deliver lines also sum to $17,200.  However, in po_line_locations_all, the amount_received value is $16,020.  As a result, the invoice is going on matching hold (this is the value Payables uses).  Does anyone know what would cause this?  Where does the value in po_line_locations_all come from?  I cannot determine how this is populated.  Any suggestions are appreciated.