Strange problem since the latest 'upgrade' for the Nvidia drivers (to 304.88).
My HTPC - Ubuntu 12.04 - is connected to my HDTV via a Samsung receiver. This receiver does all the switching for my HDMI connected devices (PS3, DVD, Satellite box, etc).
Before the Nvidia update, I had no problem switching between devices and back to the HTPC. However, now when I do this, the resolution on the HTPC changes from my preferred setting (1360 x 768) to "Auto" (which is 1920 x 1080).
I am running Gnome Shell 3.4. I have checked this in Unity and xfce and Gnome Classic, all with the same results.
Similar problem as this year old question, but I get video - No video on an Nvidia Geforce GT 440 when switching from another HDMI device