Polygon smooth mode

I render a red cube with glut. When I set the polygon mode to smooth mode by calling:
glEnable(GL_POLYGON_SMOOTH);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_DST_ALPHA);
I see black ‘stiches’ in the borders between the triangles the cube is made of.
Why is that and how can I avoid this artifact.
Many thanks,
Yossi

Yes, that’s to be expected.
See my answer in this thread for example (there are more of those): http://www.opengl.org/discussion_boards/ubb/Forum2/HTML/002510.html