@halfahundredacrewood - Please forward a copy of that Suspected Fraud email to support@e-junkie.com, so we can add that case to the ticket we opened with MTS about it. Thanks!
This issue can only affect orders where buyers go through the PayPal checkout site to pay, as that's where PayPal is failing to add the calculated tax/shipping amount(s) to the buyer's final payment total -- i.e., this only affects some buyers using the Pay Using PayPal checkout button for sellers using PayPal Payments Standard, PayPal Payments Advanced, or PayPal Payments Pro.
Buyers who use the Pay Using a Card checkout button (whether handled by a PayPal or any other payment gateway) would be unaffected, as there (unlike PayPal checkout) we have full control over calculating the final payment total and won't let buyers enter a shipping address with a different country/postal code than they'd specified in the cart.