My mk7 R did the same thing when we had a 38-40deg day in Sydney, within a couple of weeks of me picking it up. It kept the revs far higher than it should have or even needed to (power was reduced, but still plenty of torque to push through the gears during gentle driving). Odd, as you'd think higher revs would mean quicker temp buildup, but maybe it helps everything else run quicker to cool it down (fans, etc), and cope with the super high load the AC would be putting on it.
It'd be good to know for sure if it's purely mapping or overheating transmission fluid or something.