Desktop image is not showing in Mountain Lion with dual monitor I have a MBA connecting via HDMI to Samsung Monitor.
Problem is desktop background for Samsung monitor is not showing. There is only grey desktop and doesn't have any changes even I try to change the image of the desktop at System Preferences.
Changes for the MBA desktop is ok.
Is that a mountain lion bug?
Restarting the Dock seems to work for me, however I don't know what is causing this grey desktop background.

To restart the Dock, type this into Terminal and press enter:

killall Dock