Problem with MDI framework

[a_m_mukul]

Hi,

I have created one application as like follow:

MainWindow::MainWindow() : QMainWindow()
{
     QWorkspace* workspace = new QWorkspace(this);
    setCentralWidget(workspace);
    workspace->setScrollBarsEnabled(true);
 
    QGraphicsView* view = new QGraphicsView(workspace);
    workspace->addWindow(view);
    view->showMaximized();
    workspace->setActiveWindow(view);
 
}

MainWindow::MainWindow() : QMainWindow()
{
     QWorkspace* workspace = new QWorkspace(this);
    setCentralWidget(workspace);
    workspace->setScrollBarsEnabled(true);

    QGraphicsView* view = new QGraphicsView(workspace);
    workspace->addWindow(view);
    view->showMaximized();
    workspace->setActiveWindow(view);

}

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Whenever I am minimizing and then restoring the QGraphicsView window,
I am getting following message:

"QCoreApplication:: postEvent: Unexpected null receiver"

Please can any body tell me why this message might be coming.

I am working on Qt4.2.2 and Fedora core-5 application.