ItemsRepeater scrolls back to 0 when setting focus from end

[grokys]

Describe the bug

If the last item in an ItemsRepeater is brought into focus, followed by the preceding items at intervals, the ItemsRepeater occasionally scrolls back to item index 0.

Steps to reproduce the bug

    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <TextBlock Name="current"/>
        <ScrollViewer HorizontalScrollBarVisibility="Disabled"
                      VerticalScrollBarVisibility="Auto"
                      Grid.Row="1" Width="250" Height="350">
            <Border Background="LightBlue">
                <controls:ItemsRepeater x:Name="repeater">
                    <controls:ItemsRepeater.ItemTemplate>
                        <DataTemplate>
                            <Border BorderBrush="Red" BorderThickness="1">
                                <TextBlock HorizontalAlignment="Stretch" Text="{Binding}"/>
                            </Border>
                        </DataTemplate>
                    </controls:ItemsRepeater.ItemTemplate>
                </controls:ItemsRepeater>
            </Border>
        </ScrollViewer>
    </Grid>

    public sealed partial class BasicDemo : Page
    {
        readonly DispatcherTimer timer = new DispatcherTimer();
        int index;

        public BasicDemo()
        {
            this.InitializeComponent();
            repeater.ItemsSource = Enumerable.Range(0, 10000).Select(x => x.ToString()).ToList();
            timer.Interval = TimeSpan.FromMilliseconds(500);
            timer.Tick += Timer_Tick;
            timer.Start();
        }

        private void Timer_Tick(object sender, object e)
        {
            if (index == 0)
            {
                index = 9999;
            }
            else
            {
                --index;
            }

            current.Text = index.ToString();

            var element = repeater.GetOrCreateElement(index);
            element.UpdateLayout();
            element.StartBringIntoView();
        }
    }

Screenshots

Version Info

Current master (a53a650)

Windows 10 version	Saw the problem?
Insider Build (xxxxx)
May 2019 Update (18362)	Yes
October 2018 Update (17763)
April 2018 Update (17134)
Fall Creators Update (16299)
Creators Update (15063)

Device form factor	Saw the problem?
Desktop	Yes
Mobile
Xbox
Surface Hub
IoT