it's just they way most Haldex systems work, they are getting better but Haldex is still only a FWD system which can divert to the rear if required, not a true AWD system.
Some of that is even true...
On the face of it, Haldex should be a good system. 4-wheel drive on demand... and the Haldex company will tell you that it is faster than a permanent four wheel drive system at shunting the power around, it allows for better weight distribution (ever driven a proper quattro equipped Audi, they tend to be very ponderous and nose heavy because the engine sits ahead of the front wheels), it is capable of shunting up to 100% of the power rearwards - As I understand it, there is no reason why a Haldex system could not be set up to be 30:70 F:R variable between 10:90 and 50:50 depending on conditions...
Now, VAG does not like the idea of rear wheel drive cars. Remember, in the 70s Audi commissioned Porsche to design them a coupe... the resulting car was rejected, not because it was bad but only because it was rear wheel drive... that car became the 924/944/968 family and Audi came up with the first Audi Coupe.
So VAG does not like rear drive cars and as a result sets up all of it Haldex equipped cars with quite a heavy front bias (partly to reduce driveline losses - there is normally no drive to the rear) and design them for safe understeer through this and suspension setup. This is not the fault of the Haldex system but trait built into VAG cars for perceived safety... Over the years they have improved the balance but the last I drove - Audi TTS - whilst admittedly well built, fast and sure footed was still numb with understeer at the (high) limit...
