Laptop backlight keys broken in 16.10?

[Kristian Rink]

Folks;

running UbuntuGNOME 16.10 on a HP EliteBook, I can't use the device Fn hotkeys for setting display
brightness anymore. It "seems" I just can toggle between two different states of brightness (one
being "dark", one being below 25%) without actually changing display brightness. Played with various
grub settings involving ACPI backlight, neither of these approaches seemed to work.

Ideas, anyone?
TIA and all the best,
Kristian