mine did this (or something similar), it felt tacky and appeared like the surface of the grip was sort of peeling/disintigrating. I ended up using a cloth towel and rubbing all the sticky stuff off and they now seem brand new, smooth to the touch and look perfect.
I don't know if its the same thing you are seeing here, but you may test a small spot and see if just rubbing it off cleans it up. it felt on mine as if it was some kind of coating on the surface of the rubber.
i did not try any cleaner, so i can't speak to that although it might make the process easier. i wasn't sure what was happening to the grip, so i didn't apply any cleaner or chemical to the rubber and they came clean with friction so i left it at that.