linux - Cannot exit X server, restart, shutdown or drop to tty when VGA monitor active

I have a strange problem. If I connect an external VGA monitor to my laptop, exiting the X environment in any way crashes the computer.

For example, say I am working with my two monitors (the laptop's and one connected to my VGA port) active. Hitting Ctrl+Alt+F Key should take me down to a tty. What actually happens is that the VGA screen goes blank, as you would expect, but the laptop screen, although still on, shows nothing. I know the screen is on because it is slightly more illuminated than when it is off.

When in this state, I can do nothing to regain access to the machine. I have tried:

1. 
   

   Alt+F Key (and even Ctrl+Alt+F Key, just in case) combinations and none seem to have any effect.

   
   


2. 
   

   Ctrl+Alt+Del : Nothing

   
   


3. 
   

   Magic SysRq key: Nothing

   
   


4. 
   

   Blindly typing my username and password and trying to reboot/shutdown or restart GDM or MDM: Nothing

   
   

The only thing that works is a hard reset.

The exact same behavior occurs when kiling the X server through Ctrl+Alt+Backspace, rebooting or shutdown. There is no difference if I reboot/shutdown/log out using the WM's graphical menu or if I use the shutdown or rebootcommands.

It is also not WM-dependent. I have the same problem using Cinnamon, Gnome 3, MATE and xfce4.

It is, however, VGA dependent. I have tried connecting another VGA monitor and have the same problem. I do not, however, have this problem if a screen is connected to the DisplayPort. It is, therefore, a VGA specific issue.

To make things even stranger, this only occurs when both screens are active. If either the laptop screen or the VGA monitor is inactive the problem goes away.

Finally, this problem arose when I installed the latest Linux Mint Debian (LMDE). It did not occur with the previous release of LMDE. I am not sure what has changed since I used the same kernel version in both releases (I had upgraded the kernel while on the previous release) and, I think, the same nvidia drivers. Oh, and yes, I have updated the nvidia driver.

Hardware:
Dell M4500 laptop
CPU: Intel Core i7
RAM: 8GB
Graphics: nVidia GT216 [Quadro FX 880M]

Software:
LMDE, kernel 3.2.0-2-amd64
Xorg: 1.11.4
nVidia kernel: 295.20-1+3.2.9-1

Possibly relevant files:
/var/log/Xorg.0.log
~/.xsession-errors

Does anyone have any ideas how to fix this?

Answer

Well, LMDE Update Pack 5 came out yesterday. The problem was fixed when I updated my system. I don't know precisely which package was fixed but my current specs are:

LDME, kernel 3.2.0-3-amd64
Xorg: 1.12.1.902-1
nVidia kernel: 302.17+1+2+3.2.21-2

Oh well, all's well that ends well. On the assumption that it was the nvidia driver update that fixed it (though it may just as well have been xorg or the kernel upgrade) I am awarding the bounty to Stefan who needs it more than harrymc :).