KDE4 Cover Switch Effect on OS13.1 stopped working

I'm not sure what happened to break it, but for some reason my "Cover Switch Effect" stopped working on the KDE4 provided with OS13.1. I don't know if this is a 3D graphics problem, or something else. The problem may have started when I was fiddling with the Desktop Effects trying to fix a problem I was having where new windows were opening behind others, including dialog popups.

Any ideas? I'm not sure the "Defaults" button actually sets everything to defaults.