I don't think any car is good in the mud really is it unless its AWD. Mud will always cause some sort of spin just because of how slippy it is
The car has summer tyres on new, some are Bridgestones, others tend to be Dunlops. Our IS has only caused the traction control light to flicker when turning from a flat road onto a steep hill which caused one of the rear tyres to be momentarily lifted.
Summer tyres, on a cold day will slip somewhat anyway, especially if not warmed up sufficiently. Takes about 8-10 mins of constant driving for tyres to warm up (seen in an M140i)