It's happened three times to me now, that I buy one item, and it gives me the error message on the page that normally says "Thank you for your purchase!" instead of " Your page has refreshed and you're seeing this error to prevent you from buying double" or along those lines. and it turns out that it ended up buying me two of the same thing with one click, so now I'm out about 10 NY points because they repeated my clicks without my asking them to.