Braking Issue - Cayenne Hybrid

[64PW]

I bought a 2010 Cayenne Hybrid (none plug in) 4 months ago and have noticed that the brakes feel inconsistent. Most of the time i get a normal progressive feel, sometimes the pedal feels totally solid as soon as i touch it, but it brakes ok, but sometimes the pedal feels solid, then gives as a try to brake travels a short way then the brakes grab! I'm wondering if anyone else has had a similar problem? Its a very early hybrid for Porsche and wondered if this was a quirk they have since sorted? Porsche Leeds had a technician drive the car and said they could find anything wrong with it.