自定义了一个下拉表格控件，
结果点击控件执行下拉动作后一直保持下拉，
不能如常恢复不下拉的状况

Generic.xaml关键代码如下：

<Popup IsOpen="{Binding IsDropdownOpened, Mode=TwoWay, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:DropDownTable}}, UpdateSourceTrigger=PropertyChanged}" AllowsTransparency="True" MaxHeight="{Binding MaxDropdownHeight, Mode=TwoWay, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:DropDownTable}}}" Width="{TemplateBinding ActualWidth}" StaysOpen="False" PopupAnimation="Fade" MinHeight="{Binding MinDropdownHeighte, Mode=TwoWay, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type local:DropDownTable}}}" >
                                <Border Background="White" Margin="3">
                                    <ScrollViewer VerticalScrollBarVisibility="Auto" HorizontalScrollBarVisibility="Auto">
                                        <VirtualizingStackPanel x:Name="PART_ItemPanel" MaxHeight="{TemplateBinding MaxDropdownHeight}" MinHeight="{TemplateBinding MinDropdownHeight}">
                                            <DataGrid x:Name="PART_Data" DataContext="{TemplateBinding DataSource}"/>
                                        </VirtualizingStackPanel>
                                    </ScrollViewer>
                                    <Border.Effect>
                                        <DropShadowEffect BlurRadius="8" ShadowDepth="6" Opacity="0.8" Color="#FF939090" />
                                    </Border.Effect>
                                </Border>
                            </Popup>