Windows Phone 8.1 xaml, c# ComboBox does not display selection when first item is selected from full page list.

Question

I have 3 comboboxes on a xaml page and most of the time when I select the first item on the full page list displayed when the number of items are > 5, the screen returns to the combobox and the box is blank. The combobox.SelectedItem is valued but it
does not display.  This does not happen every time and I have seen this using the emulator and my windows 8.1 phone.  If I select any other item in the list they always display but when I go back and select the first item the box is blank. 
Does anyone know what I could be doing that is causing this?

Answer 1

Thanks for your help.  When I run the code below and the page is displayed, I select an item from the page list and it displays fine and then I select the first item from the page list and I do not see that selected item in the box. 
If I remove the SelectedIndex=0 it all works fine except I do not have an item selected for the initial display.  Below should show problem and should work copy/paste in universal blank app.
ScrollViewer x:Name="scrollViewer1">
        <StackPanel x:Name="stackPanel1" Background="Transparent">
            <ComboBox x:Name="comboBoxTestTypes" Margin="20,117.75,0,465.25" SelectedValuePath="ItemDescription" Width="310" Height="Auto" FontSize="17"
       ItemsSource="{Binding}" HorizontalAlignment="Left" VerticalAlignment="Center">
            <ComboBox.ItemTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding ItemDescription}" />
                </DataTemplate>
            </ComboBox.ItemTemplate>
        </ComboBox>
 </StackPanel>
    </ScrollViewer>
public sealed partial class MainPage : Page
        public ObservableCollection<ItemDetail> itemDetail;
        public MainPage()
            this.InitializeComponent();
            this.NavigationCacheMode = NavigationCacheMode.Required;
            this.itemDetail = new ObservableCollection<ItemDetail>();
        protected override void OnNavigatedTo(NavigationEventArgs e)
            PageLoad();
        public class ItemDetail
            public string ItemDescription { get; set; }
            public string ItemName { get; set; }
        private async void PageLoad()
            await initializeTypes();
            var comboBoxTestTypesItemsSource = await GetTestTypes();
            comboBoxTestTypes.ItemsSource = comboBoxTestTypesItemsSource;
            comboBoxTestTypes.SelectedIndex = 0;
        private async Task initializeTypes()
            await addTestType("Item1");
            await addTestType("Item2");
            await addTestType("Item3");
            await addTestType("Item4");
            await addTestType("Item5");
            await addTestType("Item6");
        private async Task<ObservableCollection<ItemDetail>> GetTestTypes()
            //ObservableCollection<ItemDetail> list = new ObservableCollection<ItemDetail>();
            //Random rnd = new Random();
            //for (int i = 0; i < 50; i++)
            //    list.Add(new ItemDetail() { ItemDescription = "hello" + rnd.Next(0, 1001), ItemName = rnd.Next(0, 101).ToString() });
            await getSaveDataFileDataAsync("get");
            return itemDetail;
        private async Task addTestType(string description)
            int newIdAdd = 0;
            if (itemDetail != null && itemDetail.Count > 0)
                newIdAdd = itemDetail.Max(mT => Convert.ToInt32(mT.ItemName)) + 1;
            var addTestType = new ItemDetail();
            addTestType.ItemName = newIdAdd.ToString();
            addTestType.ItemDescription = description;
            itemDetail.Add(addTestType);
            await getSaveDataFileDataAsync("save");
        private async Task getSaveDataFileDataAsync(string getSave)
            try
                DataContractJsonSerializer jsonSerializer1 = null;
                string dataFileName1 = "testFileName";
                jsonSerializer1 = new DataContractJsonSerializer(typeof(ObservableCollection<ItemDetail>));
                if (jsonSerializer1 != null && getSave == "get")
                    using (var stream1 = await ApplicationData.Current.LocalFolder.OpenStreamForReadAsync(dataFileName1))
                        itemDetail = (ObservableCollection<ItemDetail>)jsonSerializer1.ReadObject(stream1);
                if (jsonSerializer1 != null && getSave == "save")
                    using (var stream1 = await ApplicationData.Current.LocalFolder.OpenStreamForWriteAsync(dataFileName1, CreationCollisionOption.ReplaceExisting))
                            jsonSerializer1.WriteObject(stream1, itemDetail);
            catch