Why does action button in docked widget when docked with (self.addDockWidget(Qt.RightDockWidgetArea, self.dock) doesn't work in QMdiArea?

Question

The button action on dock widget doesn't activate or work when docked on right, left, top or bottom in Mdi but it works without MdiArea.

I tested without MdiArea on a tab widget and it works fine there but with Mdi it doesn't work.