ActionScript 3.0 :: Image Preloader - Using ProgressEvent Progress

I'm writing a simple image preloader and attempting to use ProgressEvent.PROGRESS on my Loader to update a simple graphic bar. All pretty standard fare so far, so I'll show you the code:

Code:
package {
import flash.display.Loader;
import flash.display.MovieClip;
import flash.display.Sprite;
import flash.events.Event;

The problem is that the "loadingProgress" function gets called twice by the aforementioned listener and so adds the ENTER_FRAME listener twice. Then, only one is removed so if I trace the value of "percentLoaded" it never stops. Is it standard that the PROGRESS event calls it's given function twice? If so, I obviously need to rethink the updating of the loader graphic.