I've a customer solution that has configured some product discounts when a voucher code is filled in the order.
During the process of checkout, the discount is always good in the cart but after the cart conclusion it duplicates the existing product discounts. I manage to see that this only happens when the flag KeepCartInContext is active. If this parameter is false it will work fine.
To help you understand the bug I've made a screencast: http://screencast.com/t/TRWcXTlF7e
The version of the solution is 8.8.1.12, but I've reproduced this also on 8.8.1.13.
Best,
Rui Silva