This bug affected me too (on Precise LTS) after purging xserver-xorg residual config once I installed xserver-xorg-lts-trusty.
I can confirm that reinstalling/reconfiguring xserver-xorg-lts-trusty fixed the problem (I used apt-get --reinstall install xserver-xorg-lts-trusty).
It took me a few hours to understand what was going on though. I agree with jerico that the bug is high impact and hard to debug for an average user.
It looks like it can affect anybody upgrading to Trusty LTS or Trusty HWE Stack.
This bug affected me too (on Precise LTS) after purging xserver-xorg residual config once I installed xserver- xorg-lts- trusty.
I can confirm that reinstalling/ reconfiguring xserver- xorg-lts- trusty fixed the problem (I used apt-get --reinstall install xserver- xorg-lts- trusty) .
It took me a few hours to understand what was going on though. I agree with jerico that the bug is high impact and hard to debug for an average user.
It looks like it can affect anybody upgrading to Trusty LTS or Trusty HWE Stack.