Can't play/stop 1 ball

Hello everyone.

Please help!

Has 2 jumping balls and 2 buttons (one stop and one play).

When use both ball - all work (push stop button - both balls stop, play button - both balls moving):

import flash.events.MouseEvent;
function ClickStop(Event:MouseEvent){
  stop();
}
stop_button.addEventListener(MouseEvent.MOUSE_UP, ClickStop);
function ClickPlay(Event:MouseEvent){
  play();
}
play_button.addEventListener(MouseEvent.MOUSE_UP, ClickPlay);

But when try to stop/play only one ball by same buttons- it does't work:

import flash.events.MouseEvent;
function ClickStop(Event:MouseEvent){
  RB.stop();
}
stop_button.addEventListener(MouseEvent.MOUSE_UP, ClickStop);
function ClickPlay(Event:MouseEvent){
  RB.play();
}
play_button.addEventListener(MouseEvent.MOUSE_UP, ClickPlay);

RB - is the instance name.

Also try a layer name.

But nothing..

Please help!