TabControl 内容不显示，点击之后才能显示？

Question

这是界面：
没显示

现在内容显示了：

这是TabControl的样式

<!--TabControl垂直样式-->
    <Style x:Key="TabControlStyleVertical" TargetType="{x:Type TabControl}">
        <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.ControlTextBrushKey}}"/>
        <Setter Property="Padding" Value="4,4,4,4"/>
        <Setter Property="BorderThickness" Value="0"/>
        <Setter Property="BorderBrush" Value="{StaticResource TabControlNormalBorderBrush}"/>
        <Setter Property="Background" Value="#F9F9F9"/>
        <Setter Property="HorizontalContentAlignment" Value="Center"/>
        <Setter Property="VerticalContentAlignment" Value="Center"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type TabControl}">
                    <Grid ClipToBounds="true" SnapsToDevicePixels="true" KeyboardNavigation.TabNavigation="Local">
                        <Grid.RowDefinitions>
                            <RowDefinition x:Name="ColumnDefinition0" Height="0.192*" />
                            <RowDefinition x:Name="ColumnDefinition1" Height="0.808*"/>
                        </Grid.RowDefinitions>
                        <Border x:Name="ContentPanel" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" 
                                Grid.Column="0" KeyboardNavigation.DirectionalNavigation="Contained" Grid.Row="1" KeyboardNavigation.TabIndex="2" KeyboardNavigation.TabNavigation="Local"  Width="Auto" Margin="0">
                            <ContentPresenter x:Name="PART_SelectedContentHost" ContentSource="SelectedContent" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" Width="Auto" Margin="0"/>
                        </Border>
                        <StackPanel x:Name="HeaderPanel" Margin="0" IsItemsHost="True" Orientation="Horizontal">
                            <StackPanel.Background>
                                <LinearGradientBrush EndPoint="0.5,1" StartPoint="0.5,0">
                                    <GradientStop Color="#7AFFFFFF" Offset="0"/>
                                    <GradientStop Color="#42F0FCFF" Offset="1"/>
                                </LinearGradientBrush>
                            </StackPanel.Background>
                        </StackPanel>
                    </Grid>
                    <ControlTemplate.Triggers>
                        <Trigger Property="IsEnabled" Value="false">
                            <Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
                        </Trigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>