drivers - Screen tearing on rotated screen in 14.04

With up-to-date Intel drivers (HD4000) on Ubuntu 14.04 with Unity, rotating the screen xrandr -o leftbreaks the vsync and induces a lot of tearing (mostly vertical one when dragging a window), I get no tearing on a non-rotated screen.

The tear-free option seems disabled:

$ cat /var/log/Xorg.0.log | grep Tear
[ 18.316] (**) intel(0): "Tear free" disabled


But in 14.04, I can't find a xorg.conf with the intel device configuration to pass the TearFree option.