When QWidget::setTabOrder is used with widgets that have a focus proxy, then depending on which order it is called, it might not get the order correct. In the attached example case, there are two container widgets, both of which have a proxy. If the order is done so that the widgets contained in the top container widget are ordered first and then the order of the two container widgets are set it will only tab between the widgets inside the top container widget.

If the setTabOrder calls are changed so it sets the order of the two container widgets and then the ones inside the top container widget, it will work correctly.