System completely inaccessible after hibernate/resume if the only enabled screen is no longer available

[Teo]

Steps to reproduce:
- connect an external monitor to a laptop
- enable only the external monitor and disable the laptop's builtin monitor
- hibernate
- disconnect the external monitor and take your laptop to another place
- resume from hibernation, ready to resume working happily with all your unsaved data

Expected behavior:
- on resume, the system should detect that the only screen that was enabled is no longer available, and that the only available screen is the builtin one, so it should enable it.

Observed behavior:
- the builtin screen is still disabled, so you have no usable screen.
- if you do have the external screen available and re-connect it, then the screen will show up on the external monitor, but the system is frozen, unresponsive to keyboard and mouse input (and doesn't even react to connecting usb devices, I can tell because if I connect an external keyboard its leds won't turn on). The only way out is a hadrware power off.

This is critical, as it causes data loss.

Last reproduced on 14.04.

ProblemType: Bug
DistroRelease: Ubuntu 12.10
Package: unity 6.12.0-0ubuntu0.2
ProcVersionSignature: Ubuntu 3.5.0-26.42-generic 3.5.7.6
Uname: Linux 3.5.0-26-generic i686
NonfreeKernelModules: nvidia
ApportVersion: 2.6.1-0ubuntu10
Architecture: i386
CompizPlugins: [core,composite,opengl,decor,vpswitch,mousepoll,compiztoolbox,snap,commands,place,resize,session,regex,grid,wall,move,gnomecompat,imgpng,animation,fade,unitymtgrabhandles,workarounds,scale,expo,ezoom,unityshell]
Date: Sun Mar 24 13:22:59 2013
InstallationDate: Installed on 2010-06-23 (1005 days ago)
InstallationMedia: Ubuntu 10.04 LTS "Lucid Lynx" - Release i386 (20100429)
MarkForUpload: True
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: unity
UpgradeStatus: Upgraded to quantal on 2013-01-13 (70 days ago)

[Andrea Azzarone (azzar1)]

Ubuntu 12.10 reached end-of-life so it's no longer supported. Can you still reproduce this bug on 14.04 (or laters)?

[teo1978 (teo8976)]

Yes I can still reproduce the issue, but it happens when HIBERNATING, not suspending (not sure whether it has changed or whether I erroneously wrote "suspend" when reporting it).

The issue is even much worse than I thought: if you happen to have the external screen available and you do re-plug it after resuming from hibernation, the output to the external screen will appear but the system will be frozen and won't respond to mouse or keyboard input. You have to switch it off via hardware.

[teo1978 (teo8976)]

I think this could be considered "confirmed", as I have already observed it on two different machines.