TabControl Duplicating Tabs

[digitall]

I am using the MVVM pattern (with MVVM light) and have a Telerik TabControl bound to a collection of ViewModels like this:

<telerik:RadTabControl x:Name="tabs" telerik:Theming.Theme="Windows7" BackgroundVisibility="Collapsed" TabStripPlacement="Left" TabOrientation="Vertical" DisplayMemberPath="Name" IsContentPreserved="True"
                                           ItemsSource="{Binding ReviewViewModels, UpdateSourceTrigger=PropertyChanged}" ContentTemplateSelector="{StaticResource ReviewTemplateSelector}" Align="Right"
                                           ItemContainerStyle="{StaticResource ReviewCategoryTabStyle}" SelectedIndex="{Binding SelectedIndex}" />

The ReviewViewModels collection is an ObservableCollection<object> because I have one static tab along with any number (generally 2-3) of user-selected tabs based on items selected in another window. Since the ViewModels are drastically different I had to be as generic as possible for the root collection and then use a ContentTemplateSelector to show the appropriate content.

The issue I have is occasionally one of the tabs is duplicated, even though the underlying source doesn't reflect this. It's very intermittent, but I just happened to catch it on my screen while working on something with the app (Phase I is still in development) and the screen showed four tabs (one was a duplicate) and when I hit a button on the view to catch in a breakpoint I could see the underlying collection only contained three total items (which was expected). I can't seem to figure out where this other item is coming from as when data retrieval is complete for the tab content I explicitely instantiate the collection at that time and loop through to add the items like this:

Dispatcher.CurrentDispatcher.Invoke(DispatcherPriority.Send, new Action(() =>
            {
                this.ReviewViewModels = new ObservableRangeCollection<object>();

                //add the categories - this is the only place the items are added
                foreach (var cat in this.ReviewCategories)
                    this.ReviewViewModels.Add(new ReviewCategoryViewModel(cat));

                //add a new notes viewmodel
                this.ReviewViewModels.Add(new ReviewNotesViewModel());

                //collection size shows three entries (two ReviewCategoryViewModel and one ReviewNotesViewModel), tabs occasionally show four at this point

                this.SelectedIndex = 0;

                this.IsBusy = false;
            }));

Any suggestions on this as to where to even start looking? I am using Q2 2011.

Edit: It just happened again and the interesting thing is the fourth tab (the duplicate) is selected even though (as indicated above) I set the selected index to 0. I hit a button on the view that takes me to the VM and did a couple of screenshots showing the data is correct:

http://www.clearsolgroup.com/images/immediate-window.png (Immediate Window - shows three total ViewModels [expected] and SelectedIndex is 0)

http://www.clearsolgroup.com/images/duplicate-tab.png (UI of the duplicate tab, with the fourth being selected even though SelectedIndex is 0 and only three ViewModels exist).

Again, this is VERY interimmittent and reproducing it is intentionally possible. It just happens occasionally.

[Vladislav]

Hi Digitall,

Unfortunately the information provided is not enough in order to reproduce and identify the problem.
Can we ask you to send us a sample project demonstrating the issue?

Thank you in advance for your cooperation.

Kind regards,
Vladislav
the Telerik team