Thanks Joe and bfg1973 for yours replies.
The tech support said:
"This behavior is normal in all keyboards A-Pro Series. This is because both the knobs and faders are analog, and requires a certain degree of inaction.
Failure to respect this margin could not have precise control of securities, and each time it is acted on one of these controls, the values were different at the same point."
Joe, I need some video to see the values changing on the right way.
Could you make it on your A-800?
I would appreciate infinitely.