I have a tab panel on a window. If, in the GUI, I initialize the window such that .visible = False, then when I show that window (by changing .visible to True), then the tab panel does not (apparently) work.
In some circumstances, resizing the window will provide a screen refresh and it appears the tab panel must have responded to the MouseDown event, but it didn’t cause a refresh.
The workaround seems to be to start the window up with .visible = True, then set it to False in code.