TabControlEx creates 2 instances of the first ContentTemplate.

[darbid]

Describe the bug

It appears that using the TabControlEx creates 2 instances of the first ContentTemplate.

I have an example and hopefully not too complicated repo of this issue. Please forgive me if my coding is the problem, however, I believe I have created a fairly standard TabControl ViewModel project.
The project creates an ObservableCollection of ViewModels and uses a TemplateSelector to find the datatemplate as indicated below.

         <DataTemplate x:Key="TabBrowserDataTemplate"
                      DataType="{x:Type local:BrowserTabItemViewModel}">
            <Grid>
                <Grid.RowDefinitions>
                    <RowDefinition Height="30" />
                    <RowDefinition Height="*" />
                </Grid.RowDefinitions>
                <Button Grid.Row="0"
                        Content="Main Tab Button" />
                <local:BrowserTabItemUC  Grid.Row="1" />
            </Grid>
        </DataTemplate>

In MainWindow.xaml I have the following TabControlEx implementation and normal TabControl implementation. You can just change over to see the difference;

                <!--<cons:TabControlEx x:Name="BrowserTabControl"
                           SelectedIndex="{Binding BrowserTabControlSelectedIndex, Mode=TwoWay}"
                           ItemsSource="{Binding TabCollection}"
                           ContentTemplateSelector="{StaticResource selector}" />-->
        <TabControl x:Name="BrowserTabControl"
                    SelectedIndex="{Binding BrowserTabControlSelectedIndex, Mode=TwoWay}"
                    ItemsSource="{Binding TabCollection}"
                    ContentTemplateSelector="{StaticResource selector}" />

If you put a break on the creation of the UserControl BrowserTabItemUC and then use either the Standard TabControl or TabControlEX you will see that TabControlEX creates 2 instances of the usercontrol, even though only 1 ViewModel was created and added to the TabControls TabCollection.