QFrame Background drawn outside frame rect when embedded in QGraphicsView

#include <QApplication>
#include <QFrame>
#include <QLabel>
#include <QVBoxLayout>
#include <QGraphicsView>
#include <QGraphicsScene>
#include <QKeyEvent>

class MyGraphicsView : public QGraphicsView
{
public:
	MyGraphicsView(QGraphicsScene *scene) : QGraphicsView(scene) { }
protected:
	void keyReleaseEvent(QKeyEvent *event);
};

void MyGraphicsView::keyReleaseEvent(QKeyEvent *event)
{
	if(event->key() == Qt::Key_S)
	{
		scale(1.10,1.10); 
	}
	else if(event->key() == Qt::Key_A)
	{
		scale(1/1.10,1/1.10); 
	}
}

int main(int argc, char ** argv)
{
	QApplication app(argc,argv);
	QFrame * mainWindow = new QFrame();
	QGraphicsScene *scene = new QGraphicsScene();
	MyGraphicsView *view = new MyGraphicsView(scene);
	QFrame *subWindow = new QFrame();
	subWindow->setGeometry(0,0,256,64);
	subWindow->setFrameShape(QFrame::Box);
	QLabel *label1 = new QLabel("Label number 1");
	QVBoxLayout *subWindowLayout = new QVBoxLayout();
	subWindowLayout->addWidget(label1);
	subWindow->setLayout(subWindowLayout);
	scene->addWidget(subWindow);
	QVBoxLayout *layout = new QVBoxLayout();
	layout->addWidget(view);
	mainWindow->setLayout(layout);
	mainWindow->setGeometry(50,50,512,256);
	mainWindow->show();
	int returnValue = app.exec();
	delete mainWindow;
                     return returnValue;
}