ContextMenu中MenuItem的header中文字展示不全

 <Border x:Name="titlePanel" HorizontalAlignment="Center" Width="100" Background="Gray"  BorderBrush="Black"  CornerRadius="3" BorderThickness="1">
        <Border.Resources>
            <SolidColorBrush x:Key="normalBorder" Color="#9fa8b7"/>
            <SolidColorBrush x:Key="hightlightBorder" Color="Red"/>
        </Border.Resources>
        <ContextMenuService.ContextMenu>
            <ContextMenu Width="120">
                <MenuItem HorizontalAlignment="Left" HorizontalContentAlignment="Left"  FontFamily="Microsoft Yahei, SimSun" FontSize="13"  x:Name="addtag">
                    <MenuItem.Icon >
                        <Image Source="skin/Images/add.png"  Width="16" Height="16"/>
                    </MenuItem.Icon>
                    <MenuItem.Header>
                        <TextBlock Text="测点添加" Width="120"  FontSize="13" />
                    </MenuItem.Header>
                </MenuItem>
                <MenuItem   FontFamily="Microsoft Yahei, SimSun" FontSize="13" x:Name="remove">
                    <MenuItem.Icon >
                        <Image Source="skin/Images/delete.png"  Width="16" Height="16"/>
                    </MenuItem.Icon>
                    <MenuItem.Header>
                        <TextBlock Text="测点" Width="100"  FontSize="13" />
                    </MenuItem.Header>
                </MenuItem>
                <Separator ></Separator>
                <MenuItem   FontFamily="Microsoft Yahei, SimSun" FontSize="13" x:Name="remove1">