Receiving Backordered PO Issue

10,0000 ordered, 7,500 received and 2,500 available to receive (aka back ordered). When they try to receive it from the scanner, it shows 7,500 / 2,500 and it will not let them receive any quantity. Usually the quantity available to receive is first

The issue was that this was a back ordered PO. We received another small shipment a day before the shipment he was trying to receive. Accounting was still invoicing the previous day's shipment and it was in a batch. Once we had them post the batch the issue went away.