Comment 9 for bug 1291371

I also confirm that problem continue to exists for Ubuntu 14.04 using th standard Linux X1 3.13.0-30-generic #54-Ubuntu SMP Mon Jun 9 22:45:01 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux kernel.

The way around it is to go the console, adjust the brightness to desired level, then go back to X. Brightness adjustment doesn't work at all when in X. Just console after I unplug the external monitor or reboot the entire machine.