As new special order sales order lines are created, the system automatically creates purchase order requisitions for each sales order line and it links these requisitions to the sales order line. If the order is modified, the existing requisitions for the line are updated (if they are still requisitions), or additional PO requisition lines are created for the additional quantity. As the PO Requisition lines are created, the system does not update the on order quantity for the item. The On Order quantity for each inventory item (the total quantity of open purchase orders and shop orders for the item) is used by the purchasing system along with the on hand, reserved and other quantities in the item to suggest a recommended quantity to purchase, and special order lines are not included as these PO lines are being used to fulfill a specific sales order.
The logic here is that since the quantity of the open special order sales order lines is not included in the inventory quantities used by purchasing, the open special order purchase order lines are not included either.