my test case:
1. from "Store East" org, create sale order type "On Credit Order" for BPartner "Store Central"
when completer document by logic of counter document and "On Credit Order", below document is create.
+ a shipment document of Store East org by rule of "On Credit Order" type.
+ shipment also make a material receipt of Store Central org as counter document (have issue report at )

+ invoice customer of Store East and a invoice vendor of "Store Central"
but
"Purchase Order Line" of invoice vendor link to sale order. i think it must link to Purchase Order is counter document of sale order.