>>Ok, so I suspect that a private variable being created that holds your data.
>>
>>You can add
>>
>>=messagebox(vartype(aaa))
>>
>>in the form's Init.
>
>I see... Thanks for your help. It's a public variable, as evidenced by DISPLAY MEMORY. I didn't know that the variables were created automagically, and the help topic for "ControlSource" doesn't mention it.

It's a very curious behavior, thanks for bringing this up.