I've been messing with appearance settings, and decided to switch from Ubuntu to Xubuntu (to see what xfce is all about). Zip, zilch, nada. Empty screen. Branch and hang. I had to do a power down and cold boot.

When I came back to Gnome, my Appearances -> Background dialog no longer responds to the mouse! It will only accept directional input from arrow keys cluster on the keyboard.

In a well-ordered universe, one might suppose this is unacceptable behavior for a "stable" OS. However in this overheated chaotic version, if anyone has any ideas how to reset normal behavior on the background selection window, I'd be grateful.