永远不会显示垂直滚动条

Question

我的垂直滚动条问题从未显示过。这是我的代码：

<ScrollViewer 
        BorderThickness="1" HorizontalScrollBarVisibility="Disabled"
        VerticalScrollBarVisibility="Visible" Padding="20">
        <Grid>

            <Grid.RowDefinitions>
                <RowDefinition Height="*" />
                <RowDefinition Height="Auto" MinHeight="100" />
            </Grid.RowDefinitions>

            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="*" MinWidth="360" />
            </Grid.ColumnDefinitions>

            <!-- Search View -->
            <ContentControl x:Name="SearchPane" Grid.Row="0" Margin="0,0,0,20" />

            <!-- Detail View -->
            <ContentControl x:Name="ActiveItem" Grid.Row="1" Margin="0" />

        </Grid>
    </ScrollViewer>

有什么想法吗？