Dynamic Image Fade - Help

I am trying to have a simple fade for my image gallery. This works perfect. Except, after I click approximately ten times, a graphic on a separate layer below my container movieClip get’s erased. It is strange becase it is just a plain graphic placed on the stage. For some reason it goes away after I click this gallery over ten clicks. Strange.


import mx.transitions.Tween;
import mx.transitions.easing.*;

var imgLevel:Number = 6000;
var attachLevel:Number = 5000;
var imgMC:String = "containerImg" + this.imgLevel;
var prevImgLevel:Number;
var prevImgMC:String;
var imageNum:Number = 1;

function nextNewImage(Void):Void {
	this.imgLevel--;
	this.imgMC = "containerImg" + this.imgLevel;
	this.prevImgLevel = this.imgLevel + 1;
	this.prevImgMC = "containerImg" + this.prevImgLevel;
	this.container_mc.createEmptyMovieClip(this.imgMC, this.imgLevel);
	this.container_mc[imgMC].attachMovie('img' + this.imageNum, 'img' + this.imgMC, this.attachLevel);
	
	// Fade out
	var imgFade:Tween = new Tween(this.container_mc[prevImgMC], '_alpha', Strong.easeOut, 100, 0, .5, true);
	this.imgFade.onMotionFinished = function(Void):Void {
		container_mc[prevImgMC].removeMovieClip();
	};
}

// Load Default Image
this.nextNewImage();

this.nextImg_mc.onRelease = function(Void):Void {
	if (imageNum == 4) {
		imageNum = 1;
	} else {
		imageNum++;
	}
	nextNewImage();	
};

this.prevImg_mc.onRelease = function(Void):Void {
	if (imageNum == 1) {
		imageNum = 4;
	} else {
		imageNum--;
	}
	nextNewImage();
};