>First, it appears to only occur when the the top, left porperties are 0

Nope, I could repro it with small numbers: 10 worked, 50 didn't.

>and AutoCenter = .F. or if the form hasn't been moved.

Yup, this is what I'm seeing.

>Second, it appears tied to the MouseMove event only when the mouse button is
>down. Placing a NODEFAULT in MouseMove prevents it from occuring.

Yep, I see this too. Thanks, George!