It would be more MVVM friendly to show/hide the XamDialogWindow using property rather than calling the Show() method. This would allow us to to bind the window state a value that is set in the ViewModel & not have to write any code behind to call Show()

ah! yes, that works. Not exactly sure why I didn't think of that before.

Thanks much!

Ok, narrowed it down to the window is being created inside a grid that is within a DockPanel from the SDK. Also, after the window is closed, it's not being distroyed so I'm checking for it in the child collection of the grid before creating a new one and re-using it.

here is the xaml:

<UserControl x:Class="TestInfragisticsDialogWindow.MainPage"

    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"

    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"

          xmlns:ig="http://schemas.infragistics.com/xaml"

    mc:Ignorable="d"

    d:DesignHeight="478" d:DesignWidth="637" xmlns:toolkit="http://schemas.microsoft.com/winfx/2006/xaml/presentation/toolkit">

    <Grid x:Name="LayoutRoot" Background="White">

        <Button Content="Button" Height="23" HorizontalAlignment="Left" Margin="62,421,0,0" Name="button1" VerticalAlignment="Top" Width="75" Click="button1_Click" />

        <toolkit:DockPanel Height="349"  Name="dockPanel1" VerticalAlignment="Top">

            <Grid x:Name="grid1" Margin="0" toolkit:DockPanel.Dock="Right" RenderTransformOrigin="0.5,0.5" HorizontalAlignment="Left" Width="637">

            </Grid>

        </toolkit:DockPanel>

    </Grid>

</UserControl>

Here is the C# code:

using System.Windows;

using System.Windows.Controls;

using Infragistics.Controls.Interactions;

namespace TestInfragisticsDialogWindow

{

    public partial class MainPage : UserControl

    {

        public MainPage()

        {

            InitializeComponent();

        }

        private void button1_Click(object sender, RoutedEventArgs e)

        {

            XamDialogWindow window = null;

            // if the window exists don't create a new one

            foreach (UIElement elem in grid1.Children)

            {

                if (elem.GetType() == typeof(XamDialogWindow))

                {

                    window = elem as XamDialogWindow;

                    if (window != null)

                        window.Visibility = System.Windows.Visibility.Visible;

                }

            }

            if (window == null)

            {

                // it doesn't exist so create a new one

                window = new XamDialogWindow();

                window.Content = "MyWindow";

                grid1.Children.Add(window);

                window.Maximize();

            }

            window.RestrictInContainer = true;

        }

    }

}