Inacurate rates issue

Hi guys, im having a issue with the rates that are displayed to a customer.

My rates in my channel manager are set at £23 per night. I have 2 promotional discounts set up. One discount for week days (Monday-Thursday) and another discount for weekend (Friday-Sunday). This gives guests rooms at £12 during the week and £14. I do this, so i can charge extra on weekend

But when a guest books a combination of a weekday and a weekend day, no discount is applied and they are charged the full £23 per night

My query is , why isnt the discount applied? Can they be stacked?