I tried 13.1 last night. still the same problems as with 12.6 with HDCP/DRM Modern apps. so I've gone back to the Windows 8 ATI drivers (labeled WDDM v1.1, 6/19/12, version 8.97.10.6).
Possible fix for ATI: 1. Right-click on the Windows Movie Maker shortcut 2. Select "Properties"
3. Click "Compatibility" tab
4. Select Windows 7 compatibility
5. Done!
Full credit to whs