I'll try the SFC later today. And yes, I do have a slideshow as my desktop.
Since a screenshot doesn't show the problem, it could very well be the drivers. (Or maybe an error in the hardware itself, but this is the only graphics corruption I've ever seen.)
When I did the initial install in December, I was using Catalyst 9.11, and then have incrementally updated the drivers with each release. (Currently running 10.5.) . I also see Catalyst 10.6 was released yesterday, so I'll update to that later today.
But since I've also been unable to consistently reproduce the error, even if a driver update was to fix it, I have no way of knowing either way unless it was to pop up again days or weeks down the road.