What causes PO Auto Source to create a new PO for the same approved requisition?

Hi

When the PO Auto Source process runs, it creates a new PO for an approved requisition and then PO Dispatches the PO to the vendor.  We didn't realize the issue until the vendor said stop sending me a new PO everyday.  Initially, the requisition was approved, a PO was created and dispatched for a dollar amount less than the requisition and then the PO was partially received (a voucher was created and payment made to the vendor).  The status of the requisition is now 'partially received'.  So, working as it should.

However, the PO Auto Source process decided it should start creating an new PO for this specific requisition every time the process runs.  And since we run PO Dispatch right afterwards, the vendor was receiving two new POs everyday until he told us to stop sending these new POs to me.  The requisition has been put on hold from further processing but what is causing PO Auto Source to continue sourcing the requisition??  Any ideas??