A very untoward bug has found an impossible hiding place in code re VFP 6

Situation: The program loads and starts running. After a few “clicks” on various forms (the # of activities vary) objects such as “List-Boxes” and “Page-Frame Tabs” will not respond. With the “List Box”
the [click-event] will not fire, but the double click-event will. “Command Buttons” normally work. Sometimes the program completely freezes.

The best reading from the debugger is “ Call stack unavailable trace between breaks is off ”

I expect there may be an illicit public variable, a bogus code “chicken-track” or perhaps a cursor blip.

I have thought of removing forms, one by one, from the “Set” as per the tedious elimination route.

Might there be a more “civilized” approach? Cheers.