Remove the commerce_order_save() from the submit as it's not necessary

pane_example/checkout_pane_example.module

@@ -145,7 +145,6 @@ function checkout_pane_example_pane_checkout_form_submit($form, &$form_state, $c
       $order->data['another_email'] = $pane_values['another_email'];
     }
     $order->data['nickname'] = $pane_values['nickname'];
-    commerce_order_save($order);
   }
 }