What happens to the received back to back PO upon cancelling the sales order

Received a back to back PO and now cancelled the respective sales order. My on hand inventory shows up the quantity received from the bac to back PO but the same quantity does not reflect on the available quantity on the order entry screen.

Resulting in discrepancy in available to transact quantity on inventory module and available quantity on Sales order entry screen.

Upon returning the quantity to supplier then quantity is same on inventory module and Sales order entry.

is this standard functionality?