I am using the Drupal 7 Commerce Authorize.Net SIM/DPM Payment Methods module. It requires a direct post to Authorize.net from the Payment section of the checkout process. My problem is on the "Review Order" page of the checkout process. When a user selects the Authorize.net DPM credit card payment option, then clicks the submit button and advances from the "Review Order" page to the "Payment" page, the shopping cart is emptied before the user enters their credit card information. Once they submit their credit card information, a receipt is emailed to the user with no products listed.
It seems like Drupal considers the submitting of the form on the "Review Order" page to be the completion of the Checkout process, and therefore empties the shopping cart. How can I get the Drupal checkout process to work properly with the Authorize.Net DPM payment method?