The following scenario causes a reliable failure:
* User adds product to cart, goes through checkout and reaches PayPal payment page
* At PayPal, user cancels transaction and is taken back to e-shop page (cart content is saved in cookies)
* Thereafter, when that user tries to check out, the page gets stuck in a loop (when you click "Proceed to confirmation", you simply end up back on the same page; you can never reach the confirmation page and finish the transaction). This problem persists over browser/session restarts.
I've seen previous reports of the checkout page getting stuck like this, which seemed to be caused by some bug with eshop's stored cookies; this appears to be a cookie-related coding bug too, since the problem is solved by deleting the cookies for the shop site. However, the user can't be expected to know that.
Would be grateful for a swift fix for this; hoping it might uncover the other reasons for "checkout loop" cookie bugs in the process.