Recently (~1 year ago) my fairly new PX-135 developed a nasty problem with a few keys (random: not the same octave, not next to each other). Specifically, if one hits one of these keys harder than a certain amount, it gets "stuck" at the highest volume (so touch response no longer works). The "fix" I found is to hit it even harder a few times in a row, and then it's back to "normal". This is not a purely electric issue - if I turn the piano off, wait, and turn it back on, the issue is still ther