Constant surplus display device detection and switching

[dronus]

Using a Thinpad T420s, after upgrading to Ubuntu 16.04, I sometimes encounter a heavy problem:

The internal screen is frequently blanking and comes up with other resolutions. This mostly triggers after resuming from standby.

Using xrandr, I figured out that there are too many display devices listed, and one of them, named VGA2, is intermittently thought to be connected, so it is automatically acitvated and the screen layout adapts, also changing the internal screen resolution (a clone view setup I guess).

In reality, there are no devices, cables or adapters attached to any display output (there is only one VGA and one DisplayPort output).

If bug kicks in, the computer is almost unusable, permanently switching the screen layout every few seconds. The bug cannot be undone by restarting Xorg and also holds after rebooting the machine.

It can be fixed by power cycling the machine.

[dronus (paul-geisler)]

Here is another different xrandr output, without any changes in the real world (eg. no display devices or cables attached at all).

This output was just taken seconds after the first.

[dronus (paul-geisler)]

Xorg log is also showing the repeated switching.