Revenue Arrangement Issue

Background: We create RA's on Sales Order (SO) creation and trigger RA's on invoicing.

Issue with foreign currency RA's: the original RA carries the originating SO exchange rate. That's fine as long as the rate does not change. Where we are invoicing a SO monthly in arrears (for example) and the system exchange rate changes, some invoices will carry the new exchange rate.

Result: the invoice posts correctly to deferred income but the revenue release from the RA, triggered by the invoice, does not assume the invoice exchange rate, thereby posting a different value to sales.

There does not appear to be any recognition of exchange rates changing where an RA is posting is triggered by a sales invoice with a different exchange rate. Is there a solution to this?