If you execute this short logo program on Windows XP with the default window size:
home clean repeat 360 [ rt 1 pd fd 1 pu fd 169 rt 72 repeat 4 [fd 170 rt 72 ] ]
one would expect the turtle to draw a small dot at the turtle's origin. This is the observed behavior when the window is made larger than the default size. At the default size, the turtle seems to "drift" when it gets near the window's edge so the turtle actually draws a line. If you make the window size larger, you can also get this code to draw a line if you add the same small number to the 169 and 170:
home clean repeat 360 [ rt 1 pd fd 1 pu fd 176 rt 72 repeat 4 [fd 177 rt 72 ] ]