Regression: Can't change screen backlight and keyboard brightness

[Alexander Browne]

With the latest updates to Artful, I can no longer change the screen backlight and keyboard brightness. The screen and keyboard brightness up/down keys don't do anything, and moving the brightness slider in Power Management doesn't do anything. (I don't know of a second way to change the keyboard brightness.) I can confirm it occurred as of 2017-08-08, but I likely just didn't notice it earlier.

It all works correctly with the Alpha 2, both in the live session and installed. I tried a clean install to make sure I didn't mess anything up, and with this second install I didn't install or configure anything except the non-free wifi driver.

I've tried the Ubuntu desktop (GNOME) daily builds from 2017-10-08 and today (2017-10-10), and everything is working normally in the live sessions, so it does seem to be Ubuntu MATE-specific.

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: ubuntu-mate-desktop 1.198
ProcVersionSignature: Ubuntu 4.11.0-10.15-generic 4.11.8
Uname: Linux 4.11.0-10-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.20.6-0ubuntu4
Architecture: amd64
CurrentDesktop: MATE
Date: Thu Aug 10 21:47:27 2017
InstallationDate: Installed on 2017-08-11 (0 days ago)
InstallationMedia: Ubuntu-MATE 17.10 "Artful Aardvark" - Alpha amd64 (20170725.1)
SourcePackage: ubuntu-mate-meta
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.