I've just tried racing the 911 around Silverstone and WOW, even on the safe default setup, it's massively prone to snap oversteer. I had quite a few epic catches in the last race, and the default setup goes from massive understeer to snap oversteer - particularly if you have even the smallest amount of lock on when you begin to turn while braking, or downshifting, from speed.
Don't know whether it's an attempt to emulate the Porsche shiftlocking on downshift (surely not, in a car that good with all that rear aero...) or whether it's just bad default setup, but it sure does make life interesting!