Printing Silverlight 4 RichTextBox content

I am using S开发者_StackOverflowilverlight 4 RichTextBox to capture data that will be printed. My problem is when I print using the code below the border surrounding the RichTextBox is also printed, even when BorderThickness is set to 0.

  PrintDocument theDoc = new PrintDocument();
            theDoc.PrintPage += (s, args) =>
            {
                args.PageVisual = MyRTB;
                args.HasMorePages = false;
            };

Sorted with BorderBrush="{x:Null}"