MaterialDesignInXAMLToolkitのDialogでコマンドのバインディングが外れてしまう ref: http://qiita.com/yu_ka1984/items/4b42872d751fe5522e5d

file0.xml

            <Button Command="{x:Static wpf:DialogHost.OpenDialogCommand}" HorizontalAlignment="Right" Margin="5,5,30,5" DockPanel.Dock="Bottom" Style="{StaticResource MaterialDesignFloatingActionAccentButton}">
                <Button.CommandParameter>
                    <StackPanel Margin="16">
                        <TextBlock>保存しますか？</TextBlock>
                        <StackPanel Orientation="Horizontal" HorizontalAlignment="Right" >
                            <Button Style="{StaticResource MaterialDesignFlatButton}"
                                        IsDefault="True"
                                        Margin="0 8 8 0"
                                        Command="{Binding SaveCommand}" CommandParameter="{Binding Model}">
                                保存
                            </Button>
                            <Button Style="{StaticResource MaterialDesignFlatButton}"
                                        IsCancel="True"
                                        Margin="0 8 8 0"
                                        Command="wpf:DialogHost.CloseDialogCommand">
                                CANCEL
                            </Button>
                        </StackPanel>
                    </StackPanel>
                </Button.CommandParameter>
                保存
            </Button>

file1.cs

        private void OpenDialogHandler(object sender, ExecutedRoutedEventArgs executedRoutedEventArgs)
        {
            if (executedRoutedEventArgs.Handled) return;

            var dependencyObject = executedRoutedEventArgs.OriginalSource as DependencyObject;
            if (dependencyObject != null)
            {
                _attachedDialogOpenedEventHandler = GetDialogOpenedAttached(dependencyObject);
                _attachedDialogClosingEventHandler = GetDialogClosingAttached(dependencyObject);
            }

            if (executedRoutedEventArgs.Parameter != null)
            {
                AssertTargetableContent();
                DialogContent = executedRoutedEventArgs.Parameter;
            }

            SetCurrentValue(IsOpenProperty, true);

            executedRoutedEventArgs.Handled = true;
        }

file2.cs

                var dialogHomeSource = executedRoutedEventArgs.Source as FrameworkElement;
                if (dialogHomeSource?.DataContext != null 
                    && !DataContext.Equals(dialogHomeSource.DataContext))
                {
                    var dialogElement = DialogContent as FrameworkElement;
                    if (dialogElement != null)
                    {
                        dialogElement.DataContext = dialogHomeSource.DataContext;
                    }
                }