CLONE - QMdiArea does not show the tab correctly when using QMdiArea::TabbedView and only adding one sub-window

Example to reproduce:

#include <QtGui>

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

    QMainWindow* pApp = new QMainWindow();
    QMdiArea* pMdi = new QMdiArea(pApp);
    pMdi->setViewMode(QMdiArea::TabbedView);
    pApp->setCentralWidget(pMdi);

    QFrame *pWidget = new QFrame();
    pMdi->addSubWindow(pWidget);

    //Uncomment the following lines to get a good solution with two widgets
    //QFrame *pWidget2 = new QFrame();
    //pMdi->addSubWindow(pWidget2);
    
    pApp->show();
    
    return a.exec();
}

With only one subwindow you can watch this:

Uncomment the declaration line of the second subwindow and all is ok.

 QFrame *pWidget2 = new QFrame();
 pMdi->addSubWindow(pWidget2);

This example is built with 5.7.0 in VC++ 2015 64bits

Thanks in advanced