Problem with saving InlineUIContainer items in a FlowDocument

Hi Everyone,

The following code is displaying correctly in a RichTextBox but when I save it and reload it, the InlineUIContainer item is missing (other text and formatting is displayed as normal):

Line line = new Line {X1 = 0yed Y1 = 0, X2 = 1, Y2 = 0, Stroke = new SolidColorBrush(Colors.Gray), Stretch = Stretch.Fill};
InlineUIContainer container = new InlineUIContainer(line, rtNotes.CaretPosition.GetInsertionPosition(LogicalDirection.Forward));
rtNotes.CaretPosition.Paragraph.Inlines.Add(container);

I am saving the FlowDocument as RTF to a string (Memo) column in a database with this code:

internal static string SaveRTF(RichTextBox richTextBox) {
	using (MemoryStream stream = new MemoryStream()) {
		TextRange range = new TextRange(richTextBox.Document.ContentStart, richTextBox.Document.ContentEnd);
		range.Save(stream, DataFormats.Rtf);
		return ASCIIEncoding.Default.GetString(stream.ToArray());
	}
}

internal static void LoadRTF(RichTextBox richTextBox, string rtf) {
	if (rtf.Length == 0) return;

	TextRange range = new TextRange(richTextBox.Document.ContentStart, richTextBox.Document.ContentEnd);
	using (MemoryStream stream = new MemoryStream()) {
		using (StreamWriter writer = new StreamWriter(stream)) {
			writer.Write(rtf);
			writer.Flush();
			stream.Seek(0, SeekOrigin.Begin);
			range.Load(stream, DataFormats.Rtf);
		}
	}
}

I've examined the FlowDocument XAML before it's saved and the InlineUIContainer seems to be missing.  Does anyone know what I'm doing wrong?

Thanks.