Quantity Remaining on Expense Receipt Traveler When Full Quantity Received

I am experiencing a sporadic issue on Receipt Travelers.

Can anyone tell me why when the full amount of the PO Line is received the Receipt Traveler indicates a Qty Remaining?

For example I have a PO for two lines; each line is quantity '1'.

Both lines are fully received yet when the Traveler prints it indicates Qty Received = '1' and Qty Remaining = '1'.

Later on when the Traveler is re-printed the Qty Remaining indicates '0'.

Thanks in advance.

Mike Anderson