Possibly problem with 4.2.0 kernel

[Bruno Wolff III]

On Sun, Jul 19, 2015 at 11:41:59 +0100,
  Russel Winder <russel at winder.org.uk> wrote:
>
>I should also note that it only affects the Intel video. If I force
>using the ATI Radeon video everything is fine. So the question is what
>have they done wrong with the Intel drivers?

There have been fixes going in for the i915 driver. I have switched back 
to the 4.1 kernel on the affected machine, but will be trying rc3 kernel 
when a build is available.