Had the same problem.
Asus zenbook UX32VD, Intel HD Graphics 4000
I'm on debian stable now.
gdm3 is 3.14.1-7
Take a look https://bugs.freedesktop.org/show_bug.cgi?id=87286
It provided an idea to try more recent version of the package.
I upgraded "xserver-xorg-video-intel" from stable 2:2.21.15-2+b2 to
testing 2:99.917-2 and it has resolved the issue.
I used aptitude with, as I recall, 3rd suggestion to resolve dependencies.
I had another issue on many other and very recent distros and still have it:
decreasing (only) brightness press key work only once, next presses get
an unknown delay (30-60 seconds) to be finished.
increasing brightness works well when pressing it many times.
True for gnom3 and kde (4, 5).
