Yeah mine jumped gears too, I had to take it apart and grease it, and put a bigger spring on it. Otherwise I'd try to shift it and it'd jump 3 gears. And then I would hit it to get the shifter plate to come up and it would unstick and shoot the button right off my shifter!
What kind of modifications does it require to use their plates, though? Looks like you have to scrap the old setup and make new brackets and such.