the user can always change their mind.
they can enter one address in the checkout form, then when they get to paypal decide that they want to ship to another dress instead, believe me, I have done this on many occasions, and with stores that where not based on eCart.
It is an inherent level of complexity by using a remote system. As a customer I Would expect that the last shipping address i decide to use is the one used for the shipment.
yes, that code is on the pp_confirm page.
the only way it will effect the store order summary behavior is by forcing it to use what was entered in the checkout form rather then what was selected in the paypal account.