Bug: midArea->setActiveSubWindow() does not work, if before set setViewMode(QMdiArea::TabbedView). Test code:

QMdiArea *midArea = new QMdiArea(this);
setCentralWidget(midArea);
//midArea->setViewMode(QMdiArea::TabbedView);
QLabel *label1 = new QLabel("first");
QMdiSubWindow *sw1 = midArea->addSubWindow(label1);
QLabel *label2 = new QLabel("second");
QMdiSubWindow *sw2 = midArea->addSubWindow(label2);
midArea->setActiveSubWindow(sw1);

After launch will be the active subwindow sw1 ("first"). But if uncommented line setViewMode(QMdiArea::TabbedView), then after launch will be the active subwindow sw2 ("second").