Encumbrance accounting flow in Procure to Pay cycle

Can someone help me with encumbrance accounting process flow in Procure to Pay cycle? As per my understanding, PO amount is reserved at PO completion. At what point this Encumbrance would be reserved? I am facing a problem, i have entered an encumbered PO and have also entered its receipt and receiving transaction. Then, I have entered an invoice that has been matched with respective receipt. System is reserving funds for this invoice. Ideally, system should reverse the encumbrance created at PO and then should create encumbrance at invoice. But in this case, it seems to be double reservation. Kindly