Discounts are calculated using the original list price (also known as the recommended retail price) as a base and not the most recent selling price.
The most recent selling price is often already discounted, i.e from a daily deal or product promotion.
This could lead to a sale product appearing as if it hasn't been discounted.
Pricing Changes in Cart/Checkout
Daily Deals and other promotional items have limited stock quantities secured and are available for a limited time only. If sold out the item/s will revert to the normal listed price.
All items which include deals and discounted items are only secured through payment and not by adding them to your cart.