How to set an arbitrary balloon position?

Question

I use Hardcodet WPF NotifyIcon to display custom balloons on any event.

If I create TaskbarIconMainWindow in xaml, then my balloon is placed next to the taskbar:

But when I create TaskbarIconin the resource file (xaml) or application class, my ball is placed above the taskbar:

Why is there a difference in behavior between these cases and how to control the position of custom balloons?

EDIT : I use the following code to verify it:

(App.xaml):

<Application x:Class="TestBalloon.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:tb="http://www.hardcodet.net/taskbar"
             StartupUri="MainWindow.xaml">
    <Application.Resources>
        <tb:TaskbarIcon x:Key="TrayIcon" ToolTipText="Created From Resources" />
    </Application.Resources>
</Application>

(App.xaml.cs):

public partial class App : Application
{
    public TaskbarIcon AppTrayIcon;

    protected override void OnStartup(StartupEventArgs e)
    {
        AppTrayIcon = (TaskbarIcon)FindResource("TrayIcon");
    }
}

(MainWindow.xaml):

<Window x:Class="TestBalloon.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:tb="http://www.hardcodet.net/taskbar"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <tb:TaskbarIcon x:Name="MainWindowTrayIcon" ToolTipText="Created in MainWindow" />

        <Button x:Name="MyButton" 
                Content="ClickMe"
                Margin="10,10,10,10"
                Click="MyButton_OnClick"/>
    </Grid>
</Window>

(MainWindow.xaml.cs):

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    private void MyButton_OnClick(object sender, RoutedEventArgs e)
    {
        FancyBalloon bal = new FancyBalloon(); // From Hardcodet WPF NotifyIcon Tutorial

        // To use TaskbarItem created in MainWindow.xaml
        //MainWindowTrayIcon.ShowCustomBalloon(bal, PopupAnimation.Slide, null);

        // To use TaskbarItem created in App.xaml
        ((App)Application.Current).AppTrayIcon.ShowCustomBalloon(bal, PopupAnimation.Slide, null);
    }
}