Win: Calling setFocus() in constructor of a child activeSubWindo w() returns NULL

When adding a child widget to QMdiArea after the main window has been shown, and this child widget has a setFocus call in its constructor, then this child will not be made the activeSubWindow and activeSubWindow will return null.
This happens only when the child is added directly using addSubWindow().
Creating a QMdiSubWindow containing the widget and calling addSubWindow with the subWindow works fine.