Glad I was able to help -- at least somewhat. But that seems weird -- the DSP turning on and off by itself like that. I'm guessing that some of the sounds may have DSP programmed into them, so that the DSP would turn on when you select one of those sounds, and then turn off when you select a sound that does not have DSP programmed into it. But the way you're describing this, it sounds like the DSP is just turning on and off by itself, at random, without you doing anything on the control panel.
That sounds like a defect, but if anyone else out there has experience with this keyboard and could explain this behavior, then please let us know! The other thing you can do, if you haven't done so already, is check the manual. There is often a trouble-shooting page or two toward the back of the manual that describes certain conditions/behavior and provides possible explanations for this behavior. Maybe this DSP issue will be listed, but that seems like a long shot.
One other possibility -- How are you powering the keyboard? Batteries? Make sure the batteries are fresh. AC adapter that did not come in the box with the keyboard? Make sure it has the proper voltage, polarity, and current ratings.