Im using the stereo dual panner for all tracks, as I find this gives me a better control of what goes into what channel in the stereofield. as of cubase 6 there seems to be a little hickup regarding this excellent feature.
this bug is not always there, it comes and goes like I dont know what…
please try to reproduce so we can have a fix asap 
- enable the stereo dual panner option in preferences (located in the VST section)
- make a new track
- create a stereo audio track (or any other stereo track, VSTi channel if you wish.)
- open the mixer, try and grab one of the panners and drag it around.
- sometimes it fails to move around when you click and drag it.
first time you grab hold of either of the pans, it works as normal, it follows the pointer where you drag the panner.
its only the second time (and after that) when you try to move either of the panners around that the panner dont want to follow. you can click at another point in the panning field, and the pan will go there, but when holding and dragging it, it dont always follow. sometimes it does, sometimes it dont. usually it dont.
same problem also occurs when doubleclicking in the panner, so you get the bigger panning window.
notes:
it seems to “reset” the bug if you put the panner back to original positions, but only for the first time you drag the panner again. after that first dragging of the panner, its back to the bugged behaviour.