On Joomla 3+ BreezingCommerce..
Purchase with Paypal works BUT the buyer gets two email notifications.
In the logs it has both entries but even though the buyer MUST log into see the cart the log has one entry for the buyer and another with the user_id as zero.
Yet, the notification emails are both correct with all the details.
I hacked the cart php to test forcing it to only send an email if the user_id > 0 and it worked however then the return from PayPal says 'No Data' rather than the thanks page.