The Open PO report I use is the standard one in the Purchases section of the reports menu. 

I'm not sure what you mean when you mention partial payments. We frequently receive items we order over the course of time and separate bills are created for each partial receipt and the bills are paid. We have done that for years and we are still able to select the PO for future receipts against it. This suddenly started the other day. 

I have attached an image. The top part of the image shows the body of the PO with the entire amount of the top and bottom items still on backorder, the second item completely received and the third item partially received. This is a very common situation for us. The bottom part of the image shows the list that pops up when I attempt to receive items without bill from the same vendor. The PO in question is PO 9974. It does not appear in the list despite the fact that there are still three open items on the PO. I will try the merge vendor to see if that does anything.

Thanks,

Scott