Double save sum error weirdness

gistfile1.txt

irb(main):023:0> order.save
   (0.1ms)  BEGIN
   (0.2ms)  SELECT SUM(`products`.`product_price`) AS sum_id FROM `products` INNER JOIN `orderedproducts` ON `products`.`id` = `orderedproducts`.`product_id` WHERE `orderedproducts`.`order_id` IS NULL
  SQL (0.1ms)  INSERT INTO `orders` (`client_id`, `created_at`, `delivery_date`, `order_total`, `updated_at`) VALUES (1, '2013-05-12 14:25:21', '2013-07-24', 0.0, '2013-05-12 14:25:21')
  SQL (0.1ms)  INSERT INTO `orderedproducts` (`created_at`, `order_id`, `product_id`, `quantity_ordered`, `updated_at`) VALUES ('2013-05-12 14:25:21', 6, 1, NULL, '2013-05-12 14:25:21')  
  SQL (0.1ms)  INSERT INTO `orderedproducts` (`created_at`, `order_id`, `product_id`, `quantity_ordered`, `updated_at`) VALUES ('2013-05-12 14:25:21', 6, 2, NULL, '2013-05-12 14:25:21')
   (47.8ms)  COMMIT
=> true
irb(main):024:0> order.save
   (0.1ms)  BEGIN
   (0.3ms)  SELECT SUM(`products`.`product_price`) AS sum_id FROM `products` INNER JOIN `orderedproducts` ON `products`.`id` = `orderedproducts`.`product_id` WHERE `orderedproducts`.`order_id` = 6
   (0.1ms)  UPDATE `orders` SET `order_total` = 20025.9607028961, `updated_at` = '2013-05-12 14:26:52' WHERE `orders`.`id` = 6
   (154.0ms)  COMMIT
=> true
irb(main):025:0>