Silverlight 4 RichTextBox and Empty Runs

Question

Does anyone know why the RichTextBox in SL4 does not apply formatting properties if the run is empty. This causes a big problem when trying to bind a toolbar to the control. It does not report what one would expect should be there.

For instance if a I have 5 lines 1) Text 2) Empty Run 3) Empty Run 4) Empty Run 5) Text

And apply a new font size to the entire box. i.e Select All -> Seleciton.ApplPropertyValue(Run.FontSize, 40);

The Fontsize property in the underlining xaml only gets applied to lines 1 & 5. When I put my cursur at line 2 it reports the old font size.