Turning off basic shaders had no effect.
Using the Singularity viewer had the same exit effect: Desktop/system graphics were corrupted and distorted, albeit in weird shades of blue and black rather than the red, yellow orange, pink shades of the other viewers.
Ok, here's a weird twist in this: If I take a screenshot of the desktop after one of the viewers has been exitted and then restart the computer so I can see what's going on, when I look at the screenshot it looks exactly like what the desktop is supposed to look like. So in effect the system is seeing what is supposed to be displayed, but what I'm seeing on my display is some kind of horrible, harish, Warhol-Picasso swirly psychedelic mess.