I don't have a digital piano, but I do use a Roland synthesizer plugged into my computer, and know that they can surprise you sometimes. Computer driven devices often have many functions that we do not use, or even know about--we can accidently trigger them when we hit a button or a combination of buttons without realizing it. Probably just as often, the machine gets a message that it isn't supposed to, or doesn't get one that it is supposed, and gets confused. When this happens, I just hit "All Notes OFF" on the pull down menu--assuming of course, that my screen is not frozen;-)