It seems as though the navigation buttons in windows 8.1 dont load the backdrop images anymore. With this msstlye, you will be able to add your own back into your theme! Located in:
Toolbars, Headers, & Rebar > Rebar > NavBar > Aero > Normal > Active > Background
Toolbars, Headers, & Rebar > Rebar > NavBar > Aero > Normal > InActive > Background
Toolbars, Headers, & Rebar > Rebar > NavBar > Aero > Max > Active > Background
Toolbars, Headers, & Rebar > Rebar > NavBar > Aero > Max > InActive > Background
All you need to do is design your backdrop that fits the the template buttons and then remove the template bg so that your button backdrop is the only thing. As a result to this, you will get a really nice looking Navigation bar as shown below. (There are 3 DPI set Images in each of the background locations)
I have attached the theme template if you would like to test this out. Oh and one more thing, this template is windows 8.1 update 1 ready. (Thanks Grim and DoubleS for the windows 8.1 update 1 fix)
-If you decide to use this template or implement into your own theme, please give proper credits by linking to this thread and who made the mod. Thanks!
~xXiNightXx Happy Theming!