sound doesn't stop SOMETIMES?

Hi... I would really  appreciate some help with this please... Thank you very much ahead of  time!!!

I have movie clip buttons with a dynamic sound withing a  slide show. Slide show consists of 3 movie clips connecting on frames  1, 300 and 900. The movie clip buttons with sound over are within the  connecting movie clips. My problem is that although the sound and  buttons work fine most of the time, sometimes, particularly if I mouse  over the button wile it's transitioning on one of the connecting frames  (300, 900), the sound doesn't stop... I'm sure I'm missing something in  the Action Script?? Here's the script I'm using for the buttons:

stop();

import  flash.display.MovieClip;
import flash.events.MouseEvent;

var  req:URLRequest = new URLRequest("blend.mp3");
var sound:Sound = new  Sound();
var controller:SoundChannel;

function  soundLoaded(event:Event):void
{
    controller = sound.play();
     controller.stop();

this.addEventListener(MouseEvent.ROLL_OVER,  playSound);
this.addEventListener(MouseEvent.ROLL_OUT, stopSound);
this.addEventListener(MouseEvent.CLICK,  onClickHandler);
this.addEventListener(MouseEvent.MOUSE_DOWN,  onPressHandler);
this.addEventListener(MouseEvent.MOUSE_UP,  onReleaseHandler);

}

// if you want a hand cursor
this.buttonMode  = true;
this.useHandCursor = true;

function  playSound(myEvent:MouseEvent) {
    trace("On");
     this.gotoAndPlay("one");
    controller = sound.play();
}
function  stopSound(myEvent:MouseEvent) {
    trace("Out");
     this.gotoAndPlay("two");
    controller.stop();

   

}
function  onClickHandler(myEvent:MouseEvent) {
    trace("I waited for Press  AND Release!!!");
    this.gotoAndPlay("three");
}
function  onPressHandler(myEvent:MouseEvent) {
    trace("Press");
}
function  onReleaseHandler(myEvent:MouseEvent) {
    trace("Release");
     this.gotoAndPlay("four");
}


sound.addEventListener(Event.COMPLETE,  soundLoaded);
sound.load(req);

Thank you!!