intercompany postings in navision 4.0

I just tested the new intercompany-feature and maybe was expecting too much or just do not know to handle it correctly, because one main scenario at our company cannot be accomplished with this new feature. The situation is as follows: DE – order → AT → invoice → DE → shipment → DE’s customer Germany sends a purchase order to Austria, where it is going to become a sales order. So far, everything works great, but then when we in Austria ship the goods (directly to their customer) and send the invoice to our german subsidiary. When we in Austria post the sales order another IC-Invoice is generated. When they in Germany import that IC-Invoice into their company they get a new invoice that is not connected to the originally purchase order. If they post the invoice, the purchase order is not affected in any way. So what is the feature about this? That really confuses me and in the Microsoft demo script they just show how to transfer invoices, not whole orders. May anybody has mor experience with this an can tell me how i can affect the originally purchas eorder with another created receivables invoice. Many thanks in advance Thomas