wpf randomly highlighting text on vista / xp

This issue only happens on vista and xp. What is happening is if there is a textbox that has a lot of text and is partially off the screen and you click in it, wpf will scroll it into view and highlight text while it does this. In windows 7 it won't scroll it into view. I am using .net 4 and have tried clearing the selection on the textbox's received focus, got keyboard focus, and mouse capture events, but the scroll seems to take place after those. I have included some screen shots of what I am talking about as well as a test app that demonstrates the problem.

Before clicking on anything, In the next screen shot all I have done was click on line 6

After clicking on line 6 you can see everything is highlighted as it scrolled the textbox into view.

repro:

/// <summary>
/// Interaction logic for MainWindow.xaml
/// </summary>
public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        for (int i = 1; i < 1000; i++开发者_如何学编程)
        {
            textBox3.AppendText(string.Format("line {0}\r\n", i));
        }
    }
}

<Window x:Class="WpfApplication1.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525" MaxHeight="350" MaxWidth="525">
<Grid>
    <ScrollViewer>
        <Grid>
            <Grid.RowDefinitions>
                <RowDefinition Height="100"></RowDefinition>
                <RowDefinition Height="auto"></RowDefinition>
                <RowDefinition Height="*"></RowDefinition>
            </Grid.RowDefinitions>
            <TextBox Grid.Row="0" Text="this is some text"></TextBox>
            <TextBox Grid.Row="1" Text="this is some text"></TextBox>
            <TextBox Grid.Row="2" ScrollViewer.CanContentScroll="True"
            ScrollViewer.VerticalScrollBarVisibility="Auto" AcceptsReturn="True"
            x:Name="textBox3"></TextBox>
        </Grid>
    </ScrollViewer>        
   </Grid>
</Window>

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Turns out from Microsoft that this is a known issue in .net 3.5 and they fixed in .net 4.0. they did not have a work around.