I have an Usercontrol with one DialogWindows like this...

<UserControl x:Class="BEBIS.Presentation.ClientUI.Sachbearbeitung.SachbearbeitungAntragstellerViewNeu"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:sys="clr-namespace:System;assembly=mscorlib"
    xmlns:ig="http://schemas.infragistics.com/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
 xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d" MinWidth="1270" MinHeight="780" BorderBrush="Blue"
    <UserControl.Resources>
        <conv:VisibilityConverter x:Key="visibilityFromBool" />

        <DataTemplate DataType="{x:Type wizard:WizardNewAntragViewModel}">
            <wizard:WizardNewAntragView />
        </DataTemplate>
    </UserControl.Resources>

    <Grid>

        <ig:XamDialogWindow MinHeight="150" Width="920" Height="740"
                                CloseButtonVisibility="Collapsed"
                                MaximizeButtonVisibility="Collapsed"
                                MinimizeButtonVisibility="Collapsed"
                                StartupPosition="Center"
                                WindowState="{Binding Path=XamDialogWindowState}"
                                IsModal="{Binding Path=ShowXamDialogWindow}"
                                Content="{Binding Path=XamDialogWindowContent}">
            <ig:XamDialogWindow.KeyboardSettings>
                <ig:KeyboardSettings AllowKeyboardNavigation="True" VerticalStep="25" HorizontalStep="25" />
            </ig:XamDialogWindow.KeyboardSettings>
        </ig:XamDialogWindow>

    </Grid>
</UserControl>

The content of the DialogWindow is bound on a ViewModel and gets the view defined in the datatemplate.

The problem is that when the viewmodel should be closed by the parent viewmodel, it is not collected by the GC.
I've analyzed this with the memprofiler 5 by RedGate and there is always the Infragistics.DialogManager.
I've attached the screen.

Thanks for help.