What makes it extra strange is that you are the only one, out of our nearly 10,000 subscribed sellers, reporting this problem, which suggests there may be something unusual about your own PayPal account in particular, so I would keep pursuing the matter with PayPal Support
I think that we don't even calculate an order total to pass to PayPal (our Developers would know about this for sure); rather, we just pass item prices with tax and shipping amounts to checkout, and PayPal calculates the payment total from those figures. If so, that would indicate that whatever is going on must be happening at PayPal's end after we hand-off the cart data to them for checkout.
This is just a lark, but by any chance might you have any sort of discounts set up in your PayPal account, or might any currency conversion be involved at all?