The flash checksum (boot with 'bank hold' pressed) brought an error so I reflashed the whole rom thing.
I post the rom-update link here because I could not find it here in the yahoo support files:
The sole error is now just the pitch bend again, which is probably also the reason why it is detuned.
But there's nothing wrong with the pitch-bend when I have the Poly in original state. Could the extra IC's on the HAWK-kit draw that extra power which deregulates the pitch circuit? My PSU is 1A