It sounds like there is some Express checkout code on the Confirm Pager that should not be there.
Open the confirm page, and go to the Server behaviors List. If there are any express checkout server behaviors listed, remove them.
The checkout page has 2 checkout buttons. The checkout with Paypal express button, and the checkout button to submit the checkout form to the confirm page. There should be code at the head of the checkout page that is triggered by the express checkout button.