Accessibility "Reduce Transparency" Setting Keeps Being Re-Enabled

I can't figure this one out. For some reason, lately, every time I restart my Mac -- or even just relaunch Dock -- the "Reduce Transparency" option in System Preferences -> Accessibility -> Display is checked (without my doing so).

If I then uncheck it, it remains unchecked until I restart. Then I go into System Preferences and find that the option has been checked again.

I'm not using Dark Menu Bar and Dock. I'm not really doing anything unusual that I can think of. I've even gone into terminal and used defaults to set reduceTransparency to false but it doesn't seem to stick.

Anyone else ever see this happen?