I saw the apparently valid JSON return value back on Nov 5th, but then I started reading up on that jsonp business and fell into a vortex of confusion. And as I lay there in the fetal position, unable to move or think, I forgot to reply back.
So anyway... I don't know what "jsonp" is doing for you; have you tried "json" only as the return type? Have you tried using the $.get() function? That works pretty well and is a bit simpler...