Hi Ray, The old man bit does not apply as you are a spring chicken really !!! If I remember the sustain amount is not only adjustable from the button but each voice also has a preset level of sustain built into the voice. This is the case with Piano, to remove the base line level of sustain which inbuilt in a true Piano you need to go into Voice edit to adjust it. If the voice is Strings you will see the base line is zero as a violin does not have sustain inbuilt in it's normal state.Hope this explains why you get this effect with Piano and like sounds, It first showed up when the GN9 organ came out back in the late 1980's.
Regards John.