(Metro) Flickering image control when bound to a singleton

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C#

WPF

C#4.0

Good morning everyone,

I recently started playing around with Metro Apps. I came up with a tiny music player. Unfortunately there is one problem.

I've the following code:

private static readonly object Locker = new object();
private static volatile BitmapImage _defaultCover;
 
private BitmapImage _cover;
public BitmapImage CoverArt 
{
  get { return _cover ?? _defaultCover; }
  set { SetProperty( ref _cover, value ); }
}

private async Task LoadThumbnailAsync( StorageFile file )
{
  if ( file == null )
  {
    return;
  }
 
  var thumb = await file.GetThumbnailAsync( ThumbnailMode.MusicView, 192, ThumbnailOptions.UseCurrentScale );
  if ( thumb.Type == ThumbnailType.Image )
  {
    var cover = new BitmapImage();
    cover.SetSource( thumb );
    CoverArt = cover;
    return;
  }
 
  if ( CoverArt == null )
  {
    lock ( Locker )
    {
      if ( CoverArt == null )
      {
        // some Bitmap manipulation here...
        InMemoryRandomAccessStream memStream = ...
        ...
        
        var cover = new BitmapImage();
        cover.SetSource( memStream );
         _defaultCover = cover;
        OnPropertyChanged( "CoverArt" );
      }
    }
  }
}

So, just in short. I'm loading the built-in cover art of some mp3s. If there's no picture I want to display a custom bitmap, that's the singleton. However, all image controls which are displaying the singleton are flickering while the audio collection is still loading (the other thumbnails are generated).

I tried already skipping the InMemoryRandomAccessStream part and just load a default png from the project folder - the result is the same. To be honest I don't have clue what's causing this behavior. Maybe someone can help me?

Thanks in advance.