Series of know issues articles are showing known issue itself about Microsoft Small Basic programming language and it's workaround.
Outlines created by Shapes.AddRectangle() and Shapes.AddEllipse() are smaller than ones for GraphicsWindow.DrawRectangle() and GraphicsWindow.DrawEllipse(). In other words the center of outlines is located on the edge of a shape for GraphicsWindow.DrawXXX() but the outer border is located on the edge for Shapes.AddXXX(). Following picture shows shapes with two types of pen widths. Light blue outlines have 20 px widths and blue outlines have 6 px widths.
One way to avoid this issue is to use narrow pen width such like 3 px or less. But most of Small Basic programmers must not matter this issue because this is the current specification of Small Basic.