Problem in dragging and move QDockWidget

Hi everybody,
I've a poblem about move a QDockWidget not directly child of the MainWindow.
What I got is a QMainWindow with several children widgets. One of those is a QTabWidget and every Tab of this widget is a QDockWidget.
Now, my problem is when I undock one of these QDockWidget it become a modal widget and I can't move it. The only thing I can do is dock it again.
Somebody can help me?

Thanks

I was able to solve the issue only by directly managing the undock event. When the undock event is emitted a QDialog object is created and the widget is set to it. When the undock event is emitted from the QDialog object, the widget is set back to the QTabWidget.