ahhh........ the world of TPMS! Great idea, bad design. I have had similar problems also with my 2010. I bet there will be a TSB soon if not already to change something?
I have heard of them breaking off inside, maybe at low speeds they get tossed around (light comes on) and then at highway speeds centrifugal force kicks in and they stay put (light goes out) Any thoughts on this theory?