My guess is that software "reacts" for this in favor of controlability, and allowing the clutch slip in the transfer case. That is also probably why that is a wet clutch: to more gracefully handle the slipping and subsequent heat. The computer knows your speed and steering angle, it probably works to decrease front drive coupling progressively as steering angle increases, unless DSC sees a need to intervene otherwise (understeer situation will transfer torque to the front wheels). In the end though, it isn't like feathering the drive clutch from a stop where you have a moving surface scrubbing against a non-moving one, this would be a comparatively minor amount of rotational deltas between front and back drives.
It would be my guess that we can pontificate ad infinitum about how the software does what it does based on our inputs given the driving dynamics at a given moment, but I'd imagine that is as close as we can ever get as I'm sure that is pretty close to the Holy Grail of BMW
It's not mechanics anymore: it is all in the software. It is fun to try to guess though!