WPF自动换行：使用自定义字体时缺少单词

<Window x:Class="Test_the_textbox_width.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="850">
<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto"/>
        <RowDefinition />
    </Grid.RowDefinitions>
    <Grid 
          HorizontalAlignment="Center">
    <TextBlock HorizontalAlignment="Left"
               Name="textBlock1"
               VerticalAlignment="Top"
               FontFamily="Pigiarniq%20Regular.ttf#Pigiarniq"
               TextWrapping="Wrap"
               FontSize="15"
               Margin="10">
        <TextBlock.Text>
             You do not need to enter both manually. Rates are calculated using true depositional 
            (uncompacted) thicknesses, rather than measured present-day thicknesses.
        </TextBlock.Text>
    </TextBlock>
    </Grid>

</Grid>

private void textBlock1_Loaded(object sender, RoutedEventArgs e)
    {
        textBlock1.Width = textBlock1.ActualWidth;
        //textBlock1.Width = Double.NaN;  //if you leave this in, you get the bad behaviour
    }