[RESOLVED] Inconsistent Rich Text Scroll

I'm in the process of writing a control to add line numbers in a picture box into a RTB. So far so good. The only problem I cannot crack is the inconsistent scrolling when dragging the VScroll with the mouse. The lines do not scroll up equally at all time (versus when clicking the thumbbox or the NC scroll area, or key/page up/down, all those seem to move lines so there is no half cut off text at the top of the RTB window. When that happens, clicking the HScroll bar seems to set the current line into full view (or out of view). I need to be able to do that programmatically, so my lines always sync up with the numbers drawn in the picture box. Even with Spy++, I can;t find the magic message that adjusts the text in the RTB so it isn't cut off at the top. Anyone have an idea how to correct this 'text cut off' problem?

Thanks!

- Kev