i'm having the same issue and have been for the last 48 hours. the problem i have is the date / time for start / finish is not selectable. it has a start date fixed (being today) and an end date fixed (being tomorrow). then, when i try to select items for the promotion, it just sends me into a never-ending loop. 

effectively, the promotions have the same outcome, but i too liked the markdown manager because it had the old price crossed out in search results with the new price visible, whereas, with the promotions, people only see the price before the promotion is applied. 

markdown manager is being discontinued, which i'm guessing this could be that going into effect.