I have this solved - for now. But since I don't know WTF is going on, the problem may re-appear.

A ComboBox becomes invisible at runtime under certain circumstances. I want it to be visible.

If, in Combo1.Init() [this is not the final name, just for testing purposes] I add:

This.AddProperty("SomeProperty")

the ComboBox becomes invisible. If I change that to:

ADDPROPERTY(This, "SomeProperty")

then it is visible, as expected. I originally used another property; A TRY/CATCH reveals no error in either case. The debugger shows that Combo1.Visible = .T., but it is still invisible. Also, this didn't happen before, on the same form. The property is not used anywhere else (I originally used another property name, but changed this to "SomeProperty" for testing purposes).

I would expect to merely need the single This.AddProperty() command; but I included some more code for testing purposes:

DODEFAULT()
LOCAL llError
TRY 
	This.AddProperty("SomeProperty")
	* ADDPROPERTY(This, "SomeProperty")
CATCH
	llError = .T.
FINALLY

ENDTRY
MESSAGEBOX(IIF(llError, "There was an error", "NO error"))
RETURN .T.

The message "NO error" is shown, but the ComboBox is still invisible.