My store uses GBP as its default currency and offers EUR and USD as alternatives. We use Super Orders and Edit Orders. Our orders are paid through Paypal Website Payments Pro (UK).

It's been absolutely fine until now and we haven't made any configuration changes, but suddenly we've had two transactions with the same strange symptoms.

Transaction #1
25th February
Order total EUR 258.84
Amount received in Paypal EUR 258.84
Amount Applied on the invoice EUR 310.61

This means there is a EUR 51.77 difference between what was paid and what the store thinks we paid. It looks as though the Amount Applied is taking the EUR value and using the same multiplier again (our store is set up to have EUR as GBP*1.2, and the value it's reporting happens to be the EUR value*1.2).

Transaction #2
26th February
Order total USD 59.95
Amount received in Paypal USD 59.95
Amount Applied on the invoice USD 99.98

Again, the difference is the multiplier used for that currency. It's mistakenly passing the USD value as GBP (default store currency) somewhere and applying the conversion again.

The data in our reports is all correct, it's just the issue means the customer has a strange balance displayed on their invoice which doesn't actually exist. I suspect it's a problem with one of our modules (or is Paypal suddenly returning data slightly differently?) but I'm not a technical enough person to isolate the culprit and sort it out. The only unusual thing about the first transaction was that the buyer had a large number of foreign accented characters in their name and many other fields; we did have a similar problem with invoices being messed up when a customer with accents checked out once before. Could this be relevant here - and why is the second customer also affected, if so? A subsequent EUR-using customer has paid for an order since without the issue recurring, and they have an accented name/address too.

Would anyone be able to point me towards a likely cause? It would be wonderful to get this bug fixed before a customer becomes confused. If you think it's specific to one of the add-ons we're using I'll narrow my search there.

I suppose I can get around it by just removing the Amount Applied information from their template entirely (we don't generally part-refund for these products), but I want to understand what's causing it if possible as it is a little worrying.