Hi,

After further investigation it appears this is a framework issue appearing whenever the SelectedIndex is being changed using StoryBoard anitmation. It can be easily reproduced using WPF TabControl and animation that changes the SelectedIndex to 1 (after the index is changed try to select the first tab again):

<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="30"/>
        <RowDefinition Height="*"/>
    </Grid.RowDefinitions>
    <Button Content="Change tab" Width="75">
        <Button.Triggers>
            <EventTrigger RoutedEvent="ButtonBase.Click">
                <BeginStoryboard>
                    <Storyboard>
                        <Int32AnimationUsingKeyFrames Storyboard.TargetProperty="(TabControl.SelectedIndex)" 
                                                    Storyboard.TargetName="tabControl">
                            <EasingInt32KeyFrame KeyTime="0" Value="1" />
                        </Int32AnimationUsingKeyFrames>
                    </Storyboard>
                </BeginStoryboard>
            </EventTrigger>
        </Button.Triggers>
    </Button>
    <TabControl x:Name="tabControl" Grid.Row="1">
        <TabItem Header="TabItem1" />
        <TabItem Header="TabItem2" />
    </TabControl>
</Grid>

Regards,
Kalin