Hello Imad,

I have investigate your sample and I can say that the behavior you encounter is expected, because when you press the close button of the pane it only hides, because this is its default PaneCloseAction and the closed event I called for the first time, after that you set its PaneCloseAction to RemovePane and executes the Close command, which cause the Closed event to fire fir the second time. My suggestion is to set the PaneCloseAction to RemovePane at the beginning, so the event could fire only once. You still will be able to clear Pane’s Content in the Closed event:

private void OnViewsCollectionChanged(object sender, NotifyCollectionChangedEventArgs e, IRegion region, TabGroupPane regionTarget)
        {
            if (e.Action == NotifyCollectionChangedAction.Add)
            {
                //Add content panes for each associated view. 
                foreach (FrameworkElement view in e.NewItems)
                {
                    if (view != null && view is UserControlBase)
                    {
                        ContentPane newContentPane = new ContentPane() { Content = view, CloseAction = PaneCloseAction.RemovePane };//, DataContext = Content };
                        //newContentPane.Content = view;

                        var headerBinding = new Binding("TabDisplayName");
                        headerBinding.Source = newContentPane.Content;
                        newContentPane.SetBinding(ContentPane.HeaderProperty, headerBinding);

                        var imageBinding = new Binding("TabImage");
                        imageBinding.Source = newContentPane.Content;
                        newContentPane.SetBinding(ContentPane.ImageProperty, imageBinding);

                        //// in closing event we will call usercontrol's CanShutdown and Shutdown methods
                        newContentPane.Closing += delegate(object o, PaneClosingEventArgs args)
                        {
                            if (view is UserControlBase)
                                args.Cancel = !((UserControlBase)view).CanShutdown();
                        };

                        //When contentPane is closed remove the associated region 
                        newContentPane.Closed += delegate(object contentPaneSender, PaneClosedEventArgs args)
                        {
                            if (view is UserControlBase)
                                ((UserControlBase)view).Shutdown();
                            OnContentPaneClosed((ContentPane)contentPaneSender, args, region);
                        };

                        regionTarget.Items.Add(newContentPane);
                    }
                }
            }
            else
            {
                if (e.Action == NotifyCollectionChangedAction.Remove)
                {
                    //Associated View has been removed => remove the associated ContentPane from XamDockManager
                    XamDockManager xamDockManager = regionTarget.FindDockManager();
                    IEnumerable<ContentPane> contentPanes = xamDockManager.GetPanes(PaneNavigationOrder.VisibleOrder);

                    foreach (ContentPane contentPane in contentPanes)
                    {
                        if (e.OldItems.Contains(contentPane.Content))
                        {
                            contentPane.Content = null;
                            contentPane.CloseAction = PaneCloseAction.RemovePane;
                            // contentPane.ExecuteCommand(ContentPaneCommands.Close);
                        }
                    }
                }
            }
        }

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