C:\Username\Directory1 Vs. C:\Users\Username\Directory1

When I use Windows Explorer to go to C:\Username\Favorites\Subdirectory1\Subdirectory2, I see different content than when I go to C:\Users\U Username\Favorites\Subdirectory1\Subdirectory2. When I open Favorites from within Internet Explorer 9, I see the content of the second case (C:\Users\U Username\Favorites\Subdirectory1\Subdirectory2). Why do I have two sets of similar, but not...