The DefaultImageSrc property doesn't show the image when it is set to a relative file path.
Reason for Decline: This is not actually a bug. When you set the DefaultImgSrc in XAML starting with "/" the Image is shown successfully. In WPF the relative image sources must begin with "/".

http://msdn.microsoft.com/en-us/library/aa970069%28v=vs.110%29.aspx