Pay when Paid on cross charges

We would like to use the Pay-when-Paid option on Supplier invoices so the hold can be released once the customer has paid the AR Invoice.

The functionality is working as long as the Supplier Invoice, the Project and Receivables invoice are all in one Operating Unit.

However for supplier invoices that result into cross charges, the AR invoice is not automatically linked to the supplier invoice, neither are we able to manually link the two.

Can someone confirm whether this should work or not?
And if so what might we have missed (see our checklist below)

- Profile 'PA: Pay When Paid' has been set