QWidget::normalGeometry() will return an invalid rect, QRect(0,0 -1x-1), when a window is maximized by the user using the window manager controls. This does not happen when calling QWidget::showMaximized() or QWidget::setWindowState(Qt::WindowStateMaximized).

Update: This is due to the fact that the window manager does not inform the window about the normal geometry when the user maximizes the window, nor is there a convention for doing so on X11. We are looking into ways to improve this.