Recently Patrick Klug put together a list that the current release of the Metro (read: .NET 4.5) Framework has when it comes to developing and porting .NET applications. Even though the problems mentioned usually have some sort of a workaround (or a dirty hack), it reminded me that I encountered one a different limitation that will fit just well in that list - the ability to reference content directly in a MediaElement through an absolute path.
How to see it?
Create a new Metro application and put a MediaElement inside your main page. Nothing too complicated by this point. Your XAML should look somewhat close to this: