System freeze when hotplug 27" monitor in Ubuntu 12.04 unstable

I'm not sure if this is a bug yet, hence the question.

I have a Dell XPS 17" laptop (1920x1080 resolution) and recently got a new Dell 27" monitor (2560x1440 res). The laptop has an nVidia discrete card, but I don't actually have it set up (i.e. I haven't got around to successfully setting up Bumblebee yet), so I'm assuming this is all on the Intel card. The external monitor is connected via a Mini Display Port to Dual-Link DVI (the Apple branded one) adapter, then via DVI cable to the monitor (it's all I have around that works).

If I boot the laptop with the external monitor connected, everything works perfectly (except the login screen goes very low res, but I can live with that). However, if I unplug it while connected, the display will go black with the mouse cursor still visible, and completely lock up. Caps lock does not go on/off, will not respond to SysRq, Ctrl+Alt+Del, switching to a different terminal (Ctrl+Alt+F1 etc.). Only a hard reboot will do the job.

The same happens in all these scenarios:
- Unplugging the monitor when booted with it connected
- "Hot" plugging the monitor after booted
- Hitting "Apply" after making changes in System Settings > Display (e.g. if I try to move the monitor positions around)

It's not a show stopper for me, I just must be careful not to do the above, which can be inconvenient sometimes.

I am not sure where to even start looking, /var/log/syslog does not seem to contain any useful information, nor does /var/log/dmesg.0 or /var/log/Xorg.0.log

If I boot from cold with the monitor attached, and avoid the Display settings, everything works perfectly - correct resolution etc.

System details follow:

$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=12.04
DISTRIB_CODENAME=precise
DISTRIB_DESCRIPTION="Ubuntu precise (development branch)"

$ lspci | grep -i vga
00:02.0 VGA compatible controller: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller (rev 09)
01:00.0 VGA compatible controller: NVIDIA Corporation Device 124d (rev ff)