Checkout process failing on its final stage after paypal has taken $$$

Hi, I've been having some major difficulties with debugging an failure at the final stage of the checkout process after the user's payment has been received by paypal express checkout gateway. The details of the transaction are never stored in the WP marketpress and so my client is having to email the user to ask their mailing address and products ordered...

I've determined through watching the post data that it looks like the initial authorization process that goes to paypal is actually being handled like a payment instead. So when the user returns back to my site they with their transaction token, Marketpress thinks "nope that token has already been used!" FAIL.

Additionally a coworker of mine noticed that switching the theme before the doing the transaction and even during the transaction allows everything to go smoothly.

Any assistance would be appreciated...

More details to come.