Thank you for great component!
I experience similar problem as P_G in post "Bug in SimpleGraph?" http://www.delphiarea.com/forum/viewtopic.php?t=218
. When you move around the drawing area using scrollbar buttons then vertical/horizontal lines are drawn. This happens only in case if you move in down/right direction. It does not matter if there is graphics in the node or not. No changes were done to source code.
You can see how it looks on the attached screenshot.