WPF Scrollviewer in ScrollViwer header Grid freezing

 

           
           <DockPanel Dock="Top" HorizontalAlignment="Stretch" Background="White"  Grid.Row="4" Grid.Column="1"  Grid.ColumnSpan="2" Margin="0">
           <ScrollViewer DockPanel.Dock="Top" 
                  CanContentScroll="True" 
                  HorizontalScrollBarVisibility="Visible" 
                  VerticalScrollBarVisibility="Disabled" 
                          Padding="0"
                  Focusable="false" >
                <Grid Margin="0">
                    <Grid.RowDefinitions>
                        <RowDefinition Height="51"/>
                        <RowDefinition  Height="*"/>
                    </Grid.RowDefinitions>
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="*"/>
                        <ColumnDefinition  Width="*"/>
                    </Grid.ColumnDefinitions>

                    <Grid   x:Name ="GridHeader" Grid.Row="0"  IsHitTestVisible="True"  Grid.Column="0" Grid.ColumnSpan="2" Background="Transparent" HorizontalAlignment="Left" VerticalAlignment="Top" Margin="0">
                        <Grid.RowDefinitions>
                            <RowDefinition Height="*"/>
                        </Grid.RowDefinitions>
                    </Grid>


                    <DockPanel Dock="Top" VerticalAlignment="Stretch" Grid.Row="1" Grid.Column="0" Grid.ColumnSpan="2" Background="White">

                        <ScrollViewer HorizontalScrollBarVisibility="Hidden" 
                      DockPanel.Dock="Top" 
                      VerticalScrollBarVisibility="Auto" 
                      VerticalAlignment="Stretch" 
                      CanContentScroll="False" 
                      Focusable="false" >

                            <Grid  x:Name="SubGrid" IsHitTestVisible="True" ScrollViewer.CanContentScroll="True">
                                <!--PreviewMouseWheel="ScrollingNeededScrollViewer_PreviewMouseWheel"-->
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition Width="*"/>
                                    <ColumnDefinition  Width="*"/>
                                </Grid.ColumnDefinitions>
                                <Grid  x:Name ="GridColumn1" ScrollViewer.CanContentScroll="True"  IsHitTestVisible="True" Grid.Row="1" Grid.Column="0" Background="Transparent" HorizontalAlignment="Left" VerticalAlignment="Top" Margin="0">
                                    <Grid.RowDefinitions>
                                        <RowDefinition Height="*"/>
                                    </Grid.RowDefinitions>
                                </Grid>

                                <Grid x:Name ="GridColumn2" IsHitTestVisible="True" Grid.Row="1" Grid.Column="1"  Background="Transparent">
                                    <Grid.RowDefinitions>
                                        <RowDefinition Height="*"/>
                                    </Grid.RowDefinitions>
                                </Grid>


                            </Grid>

                        </ScrollViewer>
                    </DockPanel>

                </Grid>
            </ScrollViewer>

        </DockPanel>