Assets appear before movie is loaded

I am loading a movie into an empty placeholder using the MovieClipLoader object.  Currently I see that if the file is large, certain assets within it (video etc) start to appear within the placeholder before the entire file is loaded.  Therefore I want to hide the placeholder until the movie is fully loaded into it.

My code is below, except that something is wrong because I am still seeing the movie's assets appearing within the placeholder, when surely the placeholder shouldn't even be visible!  Can anyone spot my mistake?!?

var my_mcl:MovieClipLoader = new MovieClipLoader();
var my_listener:Object = new Object();

my_listener.onLoadStart = function(mc) {
      preloaderStatusText._visible = true;
      preloader._visible = true;
      preloader.preloadbar._xscale = 0;
};
my_listener.onLoadProgress=function(mc,loadedBytes,totalBytes) {
      preloaderStatusText.text = "Loading content (" + Math.round(loadedBytes/totalBytes * 100) + "%)";
      preloader.preloadbar._xscale = Math.round(100*loadedBytes/totalBytes);
};
my_listener.onLoadComplete=function(mc)      {
      this.placeHolder._visible = true;
      preloaderStatusText._visible = false;
      preloader._visible = false;
};
my_listener.onLoadInit=function(mc) {
      placeHolder._width = borderOutline._width;
      placeHolder._height = borderOutline._width;
};
my_mcl.addListener(my_listener);

this.placeHolder._visible = false;
my_mcl.loadClip(fileURL, this.placeHolder);