Backlight media keys work in desktop shell, but do not actually change the backlight

Question

I purchased a laptop that shipped oem with Ubuntu15, the backlight keys worked, and the manufacturer's tools reported that all drivers are provided by the Ubuntu packages (with the exception of the video driver).

I've changed my os to Linux Mint 17.02, and installed the manufacturer's video driver.

$ cat /etc/lsb-release
DISTRIB_ID=LinuxMint
DISTRIB_RELEASE=17.2
DISTRIB_CODENAME=rafaela
DISTRIB_DESCRIPTION="Linux Mint 17.2 Rafaela"

$ uname --kernel-release
3.16.0-38-generic
$ uname --kernel-version
#52~14.04.1-Ubuntu SMP Fri May 8 09:43:57 UTC 2015

On Linux Mint, the media keys to adjust the backlight

• control the desktop shell backlight level as reported by cinnamon
• Do not change the built in displays backlight.

Things I've done:

• I've installed xbacklight which is able to control the back light level independently.
• I've added and removed the following strings from my GRUB_CMDLINE_LINUX_DEFAULT= variables (in /etc/default/grub| following each change with sudo update-grub and a reboot)
  • GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor"
  • GRUB_CMDLINE_LINUX_DEFAULT="quiet splash video.use_native_backlight=1" ^Source
  • GRUB_CMDLINE_LINUX_DEFAULT="quiet splash video.use_native_backlight=0" ^Source

• I've used sudo nvidia-xconfig, then edited /etc/X11/xorg.conf, adding to the "Screen" Selection: ^Source

  Option "RegistryDwords" "EnableBrightnessControl=1"

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The Archlinux Wiki Baclight page was a little bit too dense for me.

I have access to the oem-shipped os and I've not seen any of the changes I've made apparent in the original os's file system.