It appears that there is no entry created for revaluation on credit notes included in processing via the suggested payments routine, whereas there is if the credit note is manually allocated first 

e.g. EURO supplier.  Entered 2 invoices fx 1.00 for €100 & €200 (to keep it simple) and a credit note for €50 fx .80. Paid with fx 1.00 through suggested payments and no entries or allocation was made for revaluation.

EURO2 supplier: Entered exact same transactions as above with same fx rates, but paid manually and Sage did post a revaluation 10 which is correct.