Invoices created in both SUS & ECC

Hi Gurus,

If we use SUS and we have a GR for, say, 100 units. If I create a GR for 10 in SUS, the next time I try to do a GR in SUS, it will restrict me to 90.

However, if I create an invoice in ECC for 10, SUS doesn't know anything about this, and the supplier can create an invoice in SUS for 100, successfully. The IDoc will error out in ECC because it can't post, but the supplier won't know that, and will think they have successfully created an invoice. Obviously, the vendor shouldn't be double-billing, but I was wondering how others have handled this issue.

Regards,
Seth