By my understanding, Haldex couple can lock up to the level that torque is evenly distributed across axles, meaning 50/50 in ideal scenario. The rest of connections are open differentials. When they say it can transfer 100% to the rear, this is just clever marketing, and although it is actually truth* (I'll explain in the end), it is incorrect to claim so, as it misleads the customers to believe rear shaft has some independent connection to the engine and full control of the torque by the Haldex system. It does not, you have additional open differential, attached to existing open differential like any normal front wheel driving car.
This setup is far from perfect in slippery conditions. It needs assistance to stop spinning wheel by applying braking force to stop it from spinning and save some remaining torque for another half of differential, or let's say "third" in this case. You have felt this behavior, as it starts slapping brake pad to the brake disc, where it looses traction. Maybe it is still in the learning stage, but I suppose it is just trying to compensate worn tires on wet road. Weight distribution affects traction, when you start, from 0, most weight is at the front where engine is. When you start accelerating, more weight is transferred to the rear, but as you get the speed weight moves back to the front.
*in theory, when there is no traction, there is no torque, formula says that. So, if fronts are spinning, no torque is present there, while all existing torque is transferred to the back. This is 100%, as they claim, can happen in some conditions, but in reality I don't think so. You don't have full control over it, and you cannot with a press of a button convert such a car to the rear wheel driven vehicle.
@o6w6e6n, maybe my understanding of technical way how 4x4 is implemented to your car, can help you follow-up how it behaves on the road and is it something expected or you really suffer some malfunction.