add_action('add_to_cart_redirect', 'resolve_dupes_add_to_cart_redirect');
function resolve_dupes_add_to_cart_redirect($url = false) {
// If another plugin beats us to the punch, let them have their way with the URL
if(!empty($url)) { return $url; }
// Redirect back to the original page, without the 'add-to-cart' parameter.
// We add the 'get_bloginfo' part so it saves a redirect on https:// sites.
return get_bloginfo('wpurl').add_query_arg(array(), remove_query_arg('add-to-cart'));
}