So, it seems the MPK has a "reversed" sustain behavior, on by default. I hooked up a pedal and can reproduce the faulty behavior by pressing the button, also in Live Mode. Only difference is that in Live Mode the initial Status isn´t transfered to the patch, so it doesnt know the sustain is on ( probably because its not restarted completly). Pushing the Sustain Button twice and it shows the same behavior in Live Mode.
So problem solved for me, Probably possible to code a custom object for this behavior, but for now i just put a jack in.
Thanks for your support