I just realized that my REV2 keyboard has left and right channels swapped... if i connect my Sennheiser HD-650 headphones (yes, I've checked cabling) to the REV2's phones output, then the stereo panning is reversed... I double checked this by also connecting my headphones to my soundcard (RME AIO), and this gives the correct stereo panning when the main outs are connected to the AIO. I also checked that my speakers were correctly connected (ADAM A3X) just to check these too... they also have the right stereo panning.
Could someone please check if their REV2 also has the L/R swapped on the headphone output? ... if this is the case, then this must be a hardware design flaw... something is definitely wrong with mine. Not that I need the headphone output, i just happened to try it temporarily and discovered this.