Bug#836939: gnome-settings-daemon: Screen brightness defaults to a very low value and can't be changed with Function Keys, Applet or in System Settings

[Christophe Troestler]

I have the same problem as well as a colleague of mine who upgraded 
today.

mutter 3.20.3-2
gnome-session 3.20.2-1
gnome-settings-daemon 3.21.90-2