Unable to select the items in a Listbox after scrolling the scroll viewer in WPF

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C#

WPF

Hello,
iam unable to select the items in a Listbox after scrolling the scrollviewer in WPF.
only able to select the items up to which the listbox is displaying after that when i scroll for the next items, those are unable to select.

sample:
XAML

<ScrollViewer
 x:Name="dataScroller"
 VerticalScrollBarVisibility="Disabled"
 HorizontalScrollBarVisibility="Auto">
    <ListBox
	Name="mylistbox"
	Grid.Row="1"
	HorizontalAlignment="Stretch"
	VerticalAlignment="Bottom"
	Height="50"
	SelectionChanged="Mylistbox_SelectionChanged" />
</ScrollViewer>

<Label
Name="label1"
Content="Label"
Grid.Column="0"
Grid.Row="0"
HorizontalAlignment="Left"
VerticalAlignment="Top"
Margin="28,13,0,0"
Width="92"
Height="23" />

C# code:

Constructor

public Window1()
   {
      InitializeComponent();
      this.WindowState= WindowState.Maximized;
      List<string> mylist=new List<string> ();
      for(int i=0;i<=50;i++)
      {
        mylist.Add(" item" + i);
      }
            mylistbox.ItemsSource=mylist;
   }
void Mylistbox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
  label1.Content=mylistbox.SelectedItem.ToString();
}

Plz help how i can select the items in a listbox after scrolling to the next items in the list box

Thanks,