Donny, this has been the same since the advent of the PSR-2000. However, for me, it was never a problem. If you notice, the player is selecting voices from registrations, and it appears that he may have his sustain pedal held down, which would cause the sound/voice to carry over into the next one selected from a registration. This does not happen if you select the voice directly from the onboard user area, which is the way I did this most of the time. Same holds true if the voice is selected via the OTS setting when a variation is changed - no problem.
I guess this could be fixed with a software upgrade, but for the most part, it has never been a deal breaker for anyone contemplating purchasing a Yamaha Arranger Keyboard.
Gary