This is somewhat of a corner case, where there is a single sub-window, setViewMode(TabbedView) is called before addSubWindow(), and the latter is called before show(). The sub-window would be active, i.e. subwindow->d_func()->isActive is true and QMdiArea::aboutToActivate() is emitted, but QMA::emitSubWindowActivated() is never called for that sub-window, resulting in that sub-window shown as unmaximized/with-a-title-bar instead of as maximized/tabbed as is expected in TabbedView. Pick-to: 6.6 6.5 Fixes: QTBUG-114188 Change-Id: Ia7b2cfd07c51867707866a1f99f70129bbdc0e3e Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>