xaml window doesnt center - wpf

Question

I have a xaml (window) control which contains a grid and inside that grid, two stackpanel. The second stackpanel is set to "collapsed" per visibility. When the form loads and the button on the form is clicked, the xaml window shows up centered by setting WindowStartupLocation="CenterScreen". But when the button on the xaml is clicked to set the second stackpanel's visibility to visible, it doesn't center no more. Can anyone help resolve this issue or tell me on how to fix this?
Update: After looking closely at this, I think it may be because the visibility is set to collapsed? I've tried instead of collapsed, hidden, and it centered it but with the column being shown empty as it's used by the stackpanel.
Here are the codes:
Form1.cs
public Form1()
{
InitializeComponent();
this.StartPosition = FormStartPosition.CenterScreen;
}
private void button_Click(object sender, EventArgs e)
{
MainWindow childWindow = new MainWindow();
childWindow.Show();
}
MainWindw.xaml
<Window x:Class="ChildProject.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:views="clr-namespace:ChildProject"
Title="MainWindow"
Width="Auto"
Height="Auto"
SizeToContent="WidthAndHeight"
AllowsTransparency="False"
ResizeMode="NoResize"
WindowStyle="None"
WindowStartupLocation="CenterScreen">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="auto" />
<ColumnDefinition Width="auto" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="auto" />
<RowDefinition Height="auto" />
</Grid.RowDefinitions>
<StackPanel x:Name="stkpnlMain"
Grid.Column="0"
Grid.Row="0"
Orientation="Vertical">
<Label Content="This is suppose to display message on right ..."
FontStyle="Italic"
FontWeight="Bold"/>
<Button Content="Click Me"
Width="75"
Margin="5" Click="Button_Click" />
</StackPanel>
<StackPanel x:Name="stkpnlDisplay"
Grid.Column="1"
Grid.Row="0"
Margin="5,0,0,0"
Orientation="Vertical"
Background="YellowGreen" Visibility="Collapsed" >
<Label Content="... First now shows ..."
BorderBrush="Black"
BorderThickness="1"
Background="Yellow" />
<Label Content="Hopefully this will work"
BorderBrush="Red"
BorderThickness="3"
Margin="0,5"
Background="White" />
</StackPanel>
</Grid>
MainWindow.xaml.cs
public MainWindow()
{
InitializeComponent();
}
private void Button_Click(object sender, RoutedEventArgs e)
{
stkpnlDisplay.Visibility = Visibility.Visible;
}