Why can't a second invoice be applied to a partial receipt in EDI process R470412

I am using JDE EDI 810 inbound processing. I have partially received goods on a PO and applied an invoice correctly to that PO receipt using R470412. I do an additional partial receipt and when I create another invoice for that second receipt, I get errors when running R470412. All fields in the F4704X are exactly the same as the correctly processed PO receipt. Any thoughts?