The reason his cap hit increases is because incentives apply to all seasons of a contract. He appears to have had an all-star selection incentive of 600k.
In cap calculations, unlikely bonuses do not count against the cap. Likely bonuses do. Only bonuses that are actually achieved count against the tax. Anyway, the difference between likely and unlikely is basically whether the player did it the year before. Coming into last season, DD had not been an all-star the year before, so his cap hit was only 9.5M (since the 600k bonus was classified as unlikely). Now, heading into this coming season, he achieved all-star status last season, so it is classified as likely. As such, it counts against the cap calculations.
Incentives like this are one area that is drastically under-reported on all the salary sites. Black box for the most part.