Q: Flashing screen/corrupted update rectangles in El Capitan

I upgraded one of my older MacBook Pros to El Capitan and have been having issues with the graphics.

Everything appears to be fine initially at start up, but as soon as a load a graphically intensive application (like App Store or Facebook in Firefox), the screen display goes wacky: flashing and misaligned graphics in the update rectangles.

This seems to me to be a bug in the video driver for the nVidia GeForce 9400M.

Note: I've run Apple Hardware Test and all checks out fine with the intensive test. Also, there were no such issues with Mavericks. So, I'm pretty sure this is an El Capitan problem.

Has anybody else experienced this issue?

MacBook Pro 15" (mid-2009, 8 GB RAM, 250 GB SSD, nVidia GeForce 9400M)