It is possible to change the window state of a QWidget without being notified about such a change.

Doing something like:

QWidget parentWidget;
QWidget childWidget(&parentWidget);
childWidget.showMaximized();
childWidget.move(childWidget.pos()); // or resize(childWidget.size()) or setGeometry(childWidget.geometry())

will reset the Qt::WindowMaximized flag, but a change/move event is never sent to the widget so it's impossible to detect such a window state change.

I belive it's suffient to simply check the current geometry before changing it in QWidget::move/resize/setGeometry.