You are right on Costa, he has that reputation. The same was true for Gareth Bale. Because of his reputation for diving, calls that should have been penalties and free kicks resulted in yellow cards against him. What I never understood was how it didn't seem to keep refs from granting penalties and not giving simulation against Luis Suarez - possibly the worst diver of all time.
Another thing to consider is how the game has gone. If there has been a lot of complaining, and the game has gotten chippy, it almost makes the refs not want to call fouls, but under such circumstances, it perversely makes them more likely to give red cards for the confrontations afterwards.