I also have the same issue. I've setup a new store and downloaded the latest version of Prestashop from the site. Everythign works well appart from the Paypal module. I'm trying to use it with a Standard account. During checkout, the user is sent to Paypal, payment is processed but the new order is not registered by Prestashop. The cart is not emptied either, however, the Paypal transaction completed successfully.
I use the US/Canada module, the transaction is done in CAD, the shop is in CAD as well as the Paypal account. The site is installed on an IIS server.
Can somebody from Prestashop help us? this make a wonderful product unusable (what use is an e-commerce CMS that can't process payments?). Thank you.