[terbooter]

я тоже методом startDrag никогда не пользуюсь.
Делаю что-то подобное

private function onEnterFrame(e:Event):void {
			//TODO оптимизировать
			this.field.x = this.mouseX-this.clickPoint.x;
			this.field.y = this.mouseY-this.clickPoint.y;
 
			if (this.field.x > 0) {
				this.field.x = 0;
			}
			if (this.field.y > 0) {
				this.field.y = 0;
			}
 
			if (this.field.x < this.stage.stageWidth - this.field.width) {
				this.field.x = this.stage.stageWidth - this.field.width;
			}
			if (this.field.y < this.stage.stageHeight - this.field.height) {
				this.field.y = this.stage.stageHeight - this.field.height;
			}
 
		}