Yep, my left wiper "shudders" similar to what you're describing when I take the key out of the ignition. Also, my rear wiper just has a mind of it's own. It hasn't rained here in a while, so I know I haven't changed the wiper stick position, but periodically the rear wiper will activate on it's own. Once it wouldn't stop, and I had to stop and restart the car to get it to turn off. Another time while driving, it just wouldn't come on at all. I had to stop and restart the car to get it to work.
Damn wipers!
S