I've had my jm4 for almost 3years and have never had any issues until recently. The undo button only works occasionally, and never when I need it to. The play button does the same thing at times too. I stomp on it, try pushing it by hand, push it very gently, and sometimes I'll hit it rapidly hoping that it will engage but with no luck. If I unplug it and plug it back in it usually works once, but after that I'm back to square one. It's becoming quite a pain in the a$$ during performances. Any help would be appreciated.