Cannot set CLSD status to Production Order with non-stock item.

This problem is in ERP-6.0 with EHP7.

We have production orders with one non-stock item. The PO for that non-stock item, is fully delivered and fully invoiced. We get check-mark for Delivery-Complete field, but we don't get check-mark for Final-Invoice field, and that field is also grayed out, so we cannot even set the check-mark manually.

We are able to TECO the production order, and also settle the order. Thereafter, when we try to set status CLSD, system gives error saying, "Purchase order item & && of order &&& still without final billing indicator". But if we see the PO history, it is fully delivered and invoiced.

Any idea what is causing the above problem, and how can we resolve it (i.e. how can we set the Final-Invoice flag, and/or set the CLSE status to production order. We can delete the PO line, and then CLSE production order - but we don't see that as a correct solution.