WPF: Possible issue with SizeToContent property

Hi,

Steps:
1. Create new WPF application;
2. Add TextBox control to the MainWindow;
3. Add a Path (horizontal line) with Stretch=Fill, Width="Auto" to the same window;
4. Set the window property SizeOnContent="Width";

From that point, the MainWindow will extend to the width of the screen.  The line won't show in window.  
What I was expecting is the window shrink to fit the width of the TextBox.   Am I missing something here?

Code sample:

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525" ResizeMode="NoResize" SizeToContent="Width">
    <Grid>
    <Path Data="M40,102 L411,107" Fill="Black" Margin="0,37,0,281" Stretch="Fill" Stroke="Black" StrokeThickness="2"/>
    <TextBlock HorizontalAlignment="Left" Height="21" Margin="0" TextWrapping="Wrap" VerticalAlignment="Top" Width="62" Text="TextBlock"/>
        
    </Grid>
</Window>

Thanks,
Gabriel