Blizzard released a blue post talking about recent bugs on the Korrak's Revenge event, such as quests displaying as not completed when they've been completed.
These will be fixed as soon as possible, and once the fixes are done, they will be noted on their usual hotfixes update post.
We’re working on a couple of bugs associated with Korrak’s Revenge.First, we have a bug where the PVP user interface is displaying the Korrak’s Revenge quest as not completed, despite the quest being. Read more on wowhead.com