Login screen crashes after HDMI cable is plugged in, resumed from suspend

I have a laptop that I connect to an external monitor. After I open the lid and hit a button to wake the computer I will connect the HDMI cable for the monitor. After plugging in the HDMI, the login screen freezes intermittently so I can't type in my password. The mouse is missing and unresponsive and the keyboard doesn't type anything.

To fix this I press Ctrl-Alt-F1 and log into the terminal. I then use the command "sudo service lightdm restart" to restart the window manager. This fixes the login issue, however it also closes all of the open applications that I had on suspend, which is not desirable.

Sometimes, after typing in my password once I've restarted lightdm, the display will get locked into a weird "refresh" state, where the user session doesn't start and the screen is stuck with no window manager, no dash, and the background is partially on both screens.

If the computer gets into this weird display mode then the only fix is to reboot. I would like to be able to plug in the HDMI from a sleep and be assured that the computer can recover the running session without crashing the login screen or the display manager.

Repro steps:

- Close laptop lid to put it to sleep
- Connect HDMI cable
- Open lid and press button (optionally, open lid then connect cable)

Graphics:

- Intel HD 4000

Computer:

- Lenovo Yoga Pro 2

ProblemType: Bug
DistroRelease: Ubuntu 14.10
Package: lightdm 1.12.3-0ubuntu1
ProcVersionSignature: Ubuntu 3.16.0-34.45-generic 3.16.7-ckt8
Uname: Linux 3.16.0-34-generic x86_64
ApportVersion: 2.14.7-0ubuntu8.2
Architecture: amd64
CurrentDesktop: Unity
Date: Tue Apr 7 07:14:29 2015
EcryptfsInUse: Yes
InstallationDate: Installed on 2014-12-18 (110 days ago)
InstallationMedia: Ubuntu 14.10 "Utopic Unicorn" - Release amd64 (20141022.1)
SourcePackage: lightdm
UpgradeStatus: No upgrade log present (probably fresh install)