Hardware: ThinkPad T550 with i7-5600U/HD5500/i915/3K display
Versions: xf86-video-intel 2.99.917, using SNA
          xorg-server 1.17.1
          linux 3.19/4.0rc5

When killing the active X session and returning to the VT, or when changing from an X session to a different VT, the display starts to drift and flicker: https://youtu.be/Mez3XlMkK-o . The display goes completely black eventually, with small flickers of data here and there when trying to change VT for example.

Can be reproduced with xf86-video-intel > 2.99.914. There seems to be some difference with what kernel is used. On 3.19 the display breaks most of the time when killing the X session, but not when changing from a X session to another VT. On 4.0rc5 the display always breaks both when switching from a X session to another VT and when killing the X session.

After the display drift has started, starting a new X session, trying to switch back to existing X session, etc, does not help recovering from the problem. In addition to a reboot, suspending and resuming seems to stop it.

The problem is not present when using UXA, or when using modesetting driver instead of intel. Arch Linux was used for testing, with matching xorg-server version (1.17.1 for >2.99.914, 1.16.0 when testing with 2.99.914).

Reverting git commit 57bf3d ("sna: Disable the fb on switching away from X") seems to solve the issue.