I am not sure what is going on, since I don't use cloth much at all myself. Did you check with the list at the wiki on cloth collisions
? That list helped me out when I was playing with cloth a few months ago. My problem at the time was with layers, but I don't think that is your problem here since it is hitting it when it is not moving.
Usually the solution I end up having is to completely re-bake the simulation, whether it's cloth, fluids, or some other simulation. If that doesn't help and that list doesn't help, I'm not sure what could be wrong.