In using the ext:Desktop I noticed that if by chance the wallpaper file, as referenced by the Wallpaper attribute, was not present the control will endlessly try to look for it, essentially freezing the application.

This is not necessarily a bug but I believe that holding up the entire page just for the sake of the wallpaper might not be the best thing. Could the control, if the wallpaper file isn't found, simply default to the standard Window's blue background color instead?