My MBP has started to change the brightness randomly. I think it mostly happens when waking from sleep.
The MBP is calibrated to a brightness value of 120, but suddenly changes to very low or fully lit.
NO - I have not set the preferences to " Automatically adjust to ambient light "
My ext. monitor has no problems staying the same level.
I found this in the console log:
Jul 17 22:33:24 sren-steffens-macbook-pro [0x0-0x1c01c].com.apple.systempreferences[176]: objc[176]: Class O3Panel is implemented in both /System/Library/MonitorPanels/AppleDisplay.monitorPanels/Contents/Resources/Contrast.monitorPanel/Contents/MacOS/Contrast and /System/Library/MonitorPanels/AppleDisplay.monitorPanels/Contents/Resources/Geometry.monitorPanel/Contents/MacOS/Geometry. Using implementation from /System/Library/MonitorPanels/AppleDisplay.monitorPanels/Contents/Resources/Geometry.monitorPanel/Contents/MacOS/Geometry.