at line 290:
if ((($_SERVER["REQUEST_METHOD"] == "POST") && (isset($_SERVER["HTTP_REFERER"]) && strpos(urldecode($_SERVER["HTTP_REFERER"]), urldecode($_SERVER["SERVER_NAME"].$_SERVER["PHP_SELF"])) > 0) && isset($_POST))) {
change the trigger for the email to use the payment submit button:
if (isset($_POST["Payment_submit"]) || isset($_POST["Payment_submit_x"])) // Trigger
{
to match what is used by the other behaviors on the page.