Comment 8 for bug 812638

I'm having similar problems with my t420s with the intel integrated video, though it only happens when I attempt to connect an external monitor. The failure is intermittent and suspend/resume seems to clear up the issue ( reloading the module? ). Vague steps to reproduce:

1. Plug in external monitor to vga port
2. Wait for screen flash
3. Laptop monitor has abnormal screen ratio
4. Reset resolutions to recommended for both (1920x1200 and 1600x900) in gnome-display-settings
5. Fully blank or partially blank screen on the laptop while the external continues to work

Please let me know if there's anything you'd like me to try on my machine or information that would be useful for this type of post ( lspci/dmesg output) and apologies for the lack of detail. I'll try updating the kernel from the canonical teams ppa to see if I have any results.