class MainWindow : public QMainWindow
{
    Q_OBJECT
public:
    explicit MainWindow(QWidget *parent = 0) : QMainWindow(parent)
    {
        QMdiArea *mdi = new QMdiArea(this);
        mdi->setViewMode(QMdiArea::TabbedView);
        setCentralWidget(mdi);

        QTextEdit* edit_1 = new QTextEdit(this);
        edit_1->setWindowTitle("edit_1");
        QMdiSubWindow* window1 = mdi->addSubWindow(edit_1);
        edit_1->show();

        QTextEdit* edit_2 = new QTextEdit(this);
        edit_2->setWindowTitle("edit_2");
        QMdiSubWindow* window2 = mdi->addSubWindow(edit_2);
        edit_2->show();
        //now window2 is activeted

        //mdi->removeSubWindow(window1); // works fine
        mdi->removeSubWindow(window2);
    }
};