GUI changes brightness in wrong /sys/class/backlight/*/brightness

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http://askubuntu.com – When I use Fn+F6 / F7 (brighness down and up on Toshiba) the brightness notification opens up and responds, but the actual screen brightness remains unchanged. When I go to Settings > Brightness and adjust the slider, the same happens. lspci reports my single graphics card: 01:00.0 VGA compatible controller: Advanced Micro Devices [AMD] nee ATI Mobility Radeon HD 2400 I noticed both actions are taking effect on /sys/class/backlight/toshiba/brightness. When I manually change /sys/class/backlight/acpi_video0/brightness though, the screen finally lightens/darkens accordingly. toshset reports " (HowTos)