The values that you are updating on the confirm page are in the checkout form. These posted values are also used in the store order summary server behavior as well as the store order details. This should resolve the problem of these values being cleared out anywhere along the way, if you use the session variables it should not matter if the posted information is present when you are confirming the order. If you still have any problems with the store order summary or store order detail server behaviors on the confirm page after doing this please let us know so we can look into things further with you.
