When Scolllbar Down some missing style

[Watit]

First open Module please see "firstopen.jpg"
When Scolllbar Down some missing style
please see at "afterdownand up scollbar.jpg"

this my xaml.
and i have vdo
this link: https://dl.dropbox.com/u/50999266/ForWebSiteTelerik/VDO%20NEWS.avi

<telerik:RadGridView x:Name="rgvNewsGrid"
                                 AutoGenerateColumns="False"
                                 FontSize="15"
                                 GridLinesVisibility="None"
                                 IsFilteringAllowed="False"
                                 RowIndicatorVisibility="Collapsed"
                                 ScrollMode="Deferred"
                                 ShowGroupFooters="False"
                                 ShowGroupPanel="False">
                <!--  RowStyleSelector="{StaticResource rowStyleSelector}"  -->
                <telerik:RadGridView.Resources>

                    <ControlTemplate x:Key="DetailsPresenterTemplate" TargetType="telerik:DetailsPresenter">
                        <Border x:Name="DetailsBorder"
                                Background="{StaticResource background}"
                                BorderBrush="{StaticResource text}"
                                BorderThickness="0,0.5">
                            <VisualStateManager.VisualStateGroups>
                                <VisualStateGroup x:Name="DetailsStates">
                                    <VisualState x:Name="DetailsVisible">
                                        <Storyboard>
                                            <ObjectAnimationUsingKeyFrames BeginTime="00:00:00"
                                                                           Storyboard.TargetName="DetailsBorder"
                                                                           Storyboard.TargetProperty="Visibility">
                                                <DiscreteObjectKeyFrame KeyTime="00:00:00" Value="Visible" />
                                            </ObjectAnimationUsingKeyFrames>
                                        </Storyboard>
                                    </VisualState>
                                    <VisualState x:Name="DetailsCollapsed" />
                                </VisualStateGroup>
                            </VisualStateManager.VisualStateGroups>
                            <Border Background="{StaticResource background}">
                                <ContentPresenter x:Name="PART_ContentPresenter"
                                                  Margin="{TemplateBinding Padding}"
                                                  HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                                                  VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
                                                  OpacityMask="{StaticResource text}" />
                            </Border>
                        </Border>
                    </ControlTemplate>
                    <LinearGradientBrush x:Key="GridView_RowDetailsBackground" StartPoint="0.5,0" EndPoint="0.5,1">
                        <GradientStop Color="Transparent" />
                        <GradientStop Offset="0.3" Color="Transparent" />
                    </LinearGradientBrush>
                    <Style x:Key="DetailsPresenterStyle" TargetType="telerik:DetailsPresenter">
                        <Setter Property="Template" Value="{StaticResource DetailsPresenterTemplate}" />
                        <Setter Property="Visibility" Value="Collapsed" />
                        <Setter Property="IsTabStop" Value="False" />
                        <!--  <Setter Property="Background" Value="{StaticResource GridView_RowDetailsBackground}" />  -->
                        <Setter Property="Background" Value="{StaticResource background}" />
                        <Setter Property="Foreground" Value="{StaticResource text}" />
                        <Setter Property="BorderBrush" Value="{StaticResource ControlInnerBorder}" />
                        <Setter Property="BorderThickness" Value="1" />
                        <Setter Property="Padding" Value="0" />
                        <Setter Property="HorizontalContentAlignment" Value="Stretch" />
                    </Style>
                </telerik:RadGridView.Resources>
                <telerik:RadGridView.RowDetailsStyle>
                    <StaticResource ResourceKey="DetailsPresenterStyle" />
                </telerik:RadGridView.RowDetailsStyle>

                <telerik:RadGridView.Columns>
                    <telerik:GridViewToggleRowDetailsColumn />
                    <telerik:GridViewDataColumn DataMemberBinding="{Binding PublicDate}" Header="PublicDate" />
                    <telerik:GridViewDataColumn DataMemberBinding="{Binding Title}" Header="Title">
                        <telerik:GridViewColumn.CellTemplate>
                            <DataTemplate>
                                <HyperlinkButton Content="{Binding Title}"
                                                 FontSize="16"
                                                 NavigateUri="{Binding Path=Links}"
                                                 TargetName="_blank">
                                    <HyperlinkButton.FontFamily>ResoruceFont/tahoma.ttf#tahoma</HyperlinkButton.FontFamily>

                                </HyperlinkButton>
                            </DataTemplate>
                        </telerik:GridViewColumn.CellTemplate>
                    </telerik:GridViewDataColumn>
                    <telerik:GridViewDataColumn DataMemberBinding="{Binding Source}" Header="Source" />
                </telerik:RadGridView.Columns>

                <telerik:RadGridView.RowDetailsTemplate>
                    <DataTemplate>

                        <Grid Width="Auto"
                              HorizontalAlignment="Stretch"
                              VerticalAlignment="Stretch"
                              Background="Transparent">
                            <Grid.RowDefinitions>
                                <RowDefinition Height="auto" />
                                <RowDefinition Height="auto" />
                            </Grid.RowDefinitions>
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition Width="auto" />
                            </Grid.ColumnDefinitions>

                            <TextBlock Grid.Row="1"
                                       Grid.Column="0"
                                       Width="500"
                                       Height="auto"
                                       FontSize="15"
                                       Foreground="{StaticResource text}"
                                       Text="{Binding Description}"
                                       TextWrapping="Wrap">
                                <TextBlock.FontFamily>ResoruceFont/tahoma.ttf#tahoma</TextBlock.FontFamily>
                            </TextBlock>
                            <!--  RowDetailsTemplate Must Use Grid.Row="1" Because It not Show IF Grid.Row="0"  -->
                        </Grid>

                    </DataTemplate>
                </telerik:RadGridView.RowDetailsTemplate>
            </telerik:RadGridView>
        </Grid>