I am still having this problem, "....frequent occasions, an open app gets flooded with the background color and the window appears as a solid color with a border around it. Snapping it back to full screen and the app renders properly again..."
This is happening on my laptop and desktop. I have the latest AMD drivers and uninstalled ModernMix, wiped with CCleaner, and then re-installed ModernMix. None of this helped.
I have noticed one other ModernMix quirk, sometimes my windowed Metro apps will not minimize if I click the minimize icon on top right border. Click as you may and nothing happens. The only way to get the app minimized is by clicking the shortcut on the Taskbar and then it will minimize.