stopDrag not working..how come?

[pherball]

I've got a clip that runs a drag function when a 'zoom in' button is pressed. that all works well and when the image zooms in, i can click and drag it all around. Now, when i click the 'zoom out' button, i want to turn off the drag function but i can't seem to figure out how. The function is defined in a frame on the main timeline:

function dragMe(target_mc) {
  target_mc.onPress = function() {
    this.startDrag(false, -60, -40, 440, 400);
  };
  target_mc.onRelease = function() {
    this.stopDrag();
  }
  
}

and the 'zoom in' button initiates the function:

on (release) {
	_root.map_mc.scaleTo(200,0.5);
	_root.dragMe(_root.map_mc);
}

So, on the 'zoom out' button, i want to cancel the drag function. So I've got:

on (release) {
	_root.map_mc.scaleTo(100,0.5);
	_root.map_mc.slideTo(249,264, 0.5);
	_root.map_mc.stopDrag();
}

but the stopDrag(); doesn't seem to affect the movieclip. i can still drag it all around after i press the button. what am i missing?