go into PO-D....do you see (2) receivers?  
does the first one appear open and the 2nd receiver look closed?  
 
If you receive items off a PO, but still have unrec'd items then a (non closed) PO receiver is created. This receiver is for that receipt and is NOT a new and open PO. Not until the PO is closed (either by receiving the remaining items or manually thru PO-D) do you see a closed PO receiver.  
 
No need to delete the PO receiver.  It is not a duplicate of the original PO.    The  list of  multiple receivers give you a history of how and when the items were received.    
 
 
As a side note (but not relevant to your question) receivng POs after the reopening the PO has always bee QUIRKY. Some times if we unreceive something and then re receive ( after closing and reopening) we get way too many PO receivers. While this creates misleading reports and balances on PO-I-E, the job costing reports still have the correct quanity and dollars..