I have a laptop with the AMD A8-4500M APU using the HD 7640G GPU. Was working as intended prior to installing the Windows 8.1 Update and now the gamma level goes up and down on its own. The actual slider doesn't move, but the effect happens which makes text and such wash out, etc. I contacted HP and the only thing they made me do was uninstall and reinstall the Catalyst driver package, which didn't help. Only affects the LCD display and not the HDMI output.
Looking for any help that is out there.