Size of QGraphicsView::viewport() thrown off by QMenubar

This example application uses the reported size of the viewport to create a scene of the same size such that nothing is scaled and there are no Scrollbars. This normally works, but when a QMenuBar is added to the viewports reports it's size to be bigger than it actually is leading to a scene larger than the viewport.

The debug statements in this program suggest than the QMenuBar reports itself to only be 2 pixels high. The other widgets on the form adjust themselves to accommodate for 2 pixels but since this is inaccurate this leads to the wrong size being reported by viewport of itself.

#include <QApplication>

#include <QMainWindow>
#include <QMenuBar>
#include <QGraphicsView>

class QGuiMainScreen: public QMainWindow
{
public:
QGuiMainScreen();
virtual void show();

private:
QGraphicsView* m_gv;
};

#include <QLayout>
#include <QGLWidget>
#include <QDebug>

QGuiMainScreen::QGuiMainScreen() : QMainWindow()
{
QWidget *centralwidget;
QHBoxLayout *outerLayout;
QMenuBar *menuBar;
QMenu *menuSystem;

this->resize ( 1024, 768 );
centralwidget = new QWidget ( 0 );
this->setCentralWidget ( centralwidget );

menuBar = new QMenuBar ( 0 );
menuBar->setGeometry ( QRect ( 0, 0, 1024, 30 ) );
menuSystem = new QMenu ( menuBar );
menuSystem->setTitle ( "System" );
menuBar->addAction ( menuSystem->menuAction() );
this->setMenuBar ( menuBar );

outerLayout = new QHBoxLayout ( centralwidget );
outerLayout->setSpacing ( 0 );
outerLayout->setMargin ( 0 );

m_gv = new QGraphicsView ( );
m_gv->setScene ( new QGraphicsScene() );
outerLayout->insertWidget ( 0, m_gv, 1 );
}

void QGuiMainScreen::show()
{
QMainWindow::show();

// m_gv->setViewport ( new QGLWidget() );

qint32 sceneWidth = m_gv->viewport()->width();
qint32 sceneHeight = m_gv->viewport()->height();
qDebug() << "Viewport: "<< sceneWidth << sceneHeight;
qDebug() << "GraphicsView: " << m_gv->width() << m_gv->height();
qDebug() << "CentralWidget: " << this->centralWidget()>width() << this>centralWidget()->height();
qDebug() << "MainWindow: " << this->width() << this->height();

m_gv->scene()->setSceneRect ( -sceneWidth / 2, -sceneHeight / 2, sceneWidth, sceneHeight );
}

int main ( int argc, char *argv[] )
{
QApplication app ( argc, argv );

QGuiMainScreen myWnd;
myWnd.show();

return app.exec();
}