I have an issue when I call the tabifyDockWidget function.

I have several qdockwidgets in my qmainwindow. If I click in the close button then works fine, the qdockwidget disappear. But if I try to call to the tabifyDockWidget function several times with some of this qdockwidgets then the close button of them stops working. Any idea?

I am working under MacOSX with QT5.2

Thanks for answers!