>In 8.0 and previouly, the checkbox behaves poorly with a ControlSource set to a property that's null.

I see this also, and I passed it along for you.

I see the same behavior in VFP8 and VFP7. When testing with your code in VFP6 and VFP5, the controlsource value never changes from NULL when you check or uncheck the checkbox.

Thanks!