Unhappy UK customer. Anybody seen this?

I sent a few coins to the UK and shipped by USPS priority mail and they charged him 8 pounds (about $15 US) for a "Royal Mail International Handling Fee" which when he inquired they told him was actually postage due because they didn't recognize the postage label that I printed off of Paypal Shipping as valid postage. Here is a scan he sent me of my shipping label and the sticker they put on it. I'm sure I'm not the only one every to use paypal shipping to ship to the UK.
--Jerry
--Jerry

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Jeremy
President, Racine Numismatic Society 2013-2014; Variety Resource Dimes; See 6/8/12 CDN for my article on Winged Liberty Dimes; Ebay
TRUTH
I think Jeremy may have hit upon it. I have the postage value hidden as a default for various reasons. Perhaps on intl shipments I should unhide it.
I'll find a receipt for the shipping and send that to him to see if that helps.
--Jerry