Google Checkout Serial Number issue

Question

Hi,

I'm using google checkout for my website with Custom Order Processing.

I am using server-to-server posting and getting a response something like

_type=checkout-redirect &serial-number=c821326e-7caa-4d51-9b2e-48ef7ecd6423 &redirect-url=https://checkout.google.com/buy?o=shoppingcart&shoppingcart=8572098456

and the serial number in the above response is something like "821326e-7caa-4d51-9b2e-48ef7ecd6423"

As per the google's tutorial, we need to make a note of the serial number as this would be returned in the notifications.

But in the new order notification which i get, the serial number is something like

why is the serial number different in the above two cases. am i missing something?