I made it work without the selection changed event. As alternative I used a tap event:
<StackPanel Orientation="Vertical" Tap="StackPanel_Tap">
<TextBlock Text="{Binding Shortcut}" TextWrapping="Wrap" Style="{StaticResource PhoneTextExtraLargeStyle}" />
<TextBlock Text="{Binding BuildingName}" TextWrapping="Wrap" Style="{StaticResource PhoneTextSubtleStyle}" />
</StackPanel>
and in Code behind I get my listitem with:
private void StackPanel_Tap(object sender, System.Windows.Input.GestureEventArgs e)
{
// Save current POI.
Object object = (sender as StackPanel).DataContext as Object;
...}