Hey, I'm from Ask Mr. Robot
I see your DK at 0.06% under the hit cap with the default settings. Sometimes getting exactly to the cap isn't the most optimal solution. For example, let's say Haste is your best secondary stat and mastery is your worst. Since there are a limited number of ways to get exactly to the cap, it's possible you need to reforge Haste to Hit on 2 pieces of gear, which is sacrificing your best secondary stat. On the other hand, Mr. Robot would leave Haste on those items and reforge Mastery into Hit on 2 other items, and get you to 0.06% of the hit cap. That will result in more DPS.
However, Mr. Robot knows a lot of people like being capped, so he launched a new feature 2 weeks ago to force hit caps. If you open the options menu, at the very bottom there is an option to force hit caps. It's a new feature, so if it isn't working like you think it should, let me know so I can investigate any problems.