Problem
Need remove event listener.
Solution
Using removeEventListener
Detailed explanation
toy.buttonMode = toy.useHandCursor = true;
toy.addEventListener(MouseEvent.MOUSE_DOWN, dragToy);
function dragToy(event:MouseEvent):void
{
toy.startDrag();
toy.removeEventListener(MouseEvent.MOUSE_DOWN, dragToy);
toy.addEventListener(MouseEvent.MOUSE_UP, dropToy);
}
function dropToy(event:MouseEvent):void
{
toy.stopDrag();
toy.removeEventListener(MouseEvent.MOUSE_UP, dropToy);
toy.addEventListener(MouseEvent.MOUSE_DOWN, dragToy);
}
Also on first line of code i added useHandCursor, for this used buttonMode. You can use just buttonMode.

Source:
removingEventListener
