ActualWidth Binding Fail

TransmitView.xaml

<UserControl x:Class="OsgExporter.Shell.Views.TransmitView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             mc:Ignorable="d" Loaded="TransmitView_OnLoaded"
             d:DesignHeight="312" d:DesignWidth="496">
    <Grid x:Name="LayoutRoot">
        <Grid Margin="8,0,0,0" Height="Auto" VerticalAlignment="Center">
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto"/>
                <RowDefinition Height="Auto"/>
                <RowDefinition/>
            </Grid.RowDefinitions>
            <Border Grid.Row="0" BorderBrush="{DynamicResource DarkBlueBorderBrush}" BorderThickness="{DynamicResource StandardBorderThickness}" Background="{DynamicResource LightBlueBorderBackground}" Padding="{DynamicResource StandardBorderPadding}" CornerRadius="{DynamicResource StandardBorderCornerRadius}" Margin="{DynamicResource StandardBorderMargin}">
                <Grid>
                    <Grid.RowDefinitions>
                        <RowDefinition/>
                        <RowDefinition/>
                    </Grid.RowDefinitions>
                    <StackPanel Grid.Row="0" Orientation="Horizontal" HorizontalAlignment="Left" d:LayoutOverrides="HorizontalAlignment" Margin="2">
                        <Label Content="Records:" Style="{DynamicResource SimpleLabel}" VerticalAlignment="Center" Margin="2"/>
                        <TextBox Style="{DynamicResource SimpleTextBox}"  Text="{Binding Path=Records, Mode=TwoWay}" Margin="2" IsReadOnly="True" Width="100" />
                    </StackPanel>
                    <StackPanel Grid.Row="0" Orientation="Horizontal" HorizontalAlignment="Right" Margin="2">
                        <Label Content="Pages:" Style="{DynamicResource SimpleLabel}" VerticalAlignment="Center" Margin="2"/>
                        <TextBox Style="{DynamicResource SimpleTextBox}"  Text="{Binding Path=Pages, Mode=TwoWay}" Margin="2" IsReadOnly="True" Width="100" />
                    </StackPanel>
                    <StackPanel x:Name="insertStackPanel" Grid.Row="1" Orientation="Horizontal" Margin="2">
                        <Label Content="Inserts:" Style="{DynamicResource SimpleLabel}" VerticalAlignment="Center" Margin="2"/>
                        <TextBox Style="{DynamicResource SimpleTextBox}"  Text="{Binding Path=Inserts, Mode=TwoWay}" Margin="2" IsReadOnly="True" />
                    </StackPanel>
                </Grid>
            </Border>
            <Border Grid.Row="1" BorderBrush="{DynamicResource DarkBlueBorderBrush}" BorderThickness="{DynamicResource StandardBorderThickness}" Background="{DynamicResource LightBlueBorderBackground}" Padding="{DynamicResource StandardBorderPadding}" CornerRadius="{DynamicResource StandardBorderCornerRadius}" Margin="{DynamicResource StandardBorderMargin}">
                <StackPanel Orientation="Horizontal" Margin="2">
                    <Label Content="Processing Option:" Style="{DynamicResource SimpleLabel}" VerticalAlignment="Center" Margin="2"/>
                    <Label Content="{Binding Path=ProcessingOption}" Style="{DynamicResource SimpleLabel}" VerticalAlignment="Center" Margin="2"/>
                </StackPanel>
            </Border>
            <Border Grid.Row="2" BorderBrush="{DynamicResource DarkBlueBorderBrush}" BorderThickness="{DynamicResource StandardBorderThickness}" Background="{DynamicResource LightBlueBorderBackground}" Padding="{DynamicResource StandardBorderPadding}" CornerRadius="{DynamicResource StandardBorderCornerRadius}" Margin="{DynamicResource StandardBorderMargin}">
                <StackPanel Orientation="Horizontal" HorizontalAlignment="Right" Margin="2">
                    <Button Content="Upload" Style="{DynamicResource SimpleButton}" Margin="2" Width="50" Command="{Binding Path=UploadCommand}" />
                </StackPanel>
            </Border>
        </Grid>
    </Grid>
</UserControl>

just put

Width="{Binding ActualWidth, ElementName=stackPanel, Mode=OneWay}"

in the TextBox contained within insertStackPanel. When you do this, you can no longer scroll the window up and down on the right side of Blend 4.