glut solidsphere seam

I am writing an OpenGL GUI that views a glutSolidSphere simultaneously from several different positions (using GLLookAt)in several different viewports. The sphere is simultaneously rendered from three different viewing points, namely directly down each of the axes, in three separate viewports, using orthographic projections. The bizarre problem is that when viewing the sphere from directly above (i.e. down the negative y-axis), a ‘seam’ appears, which looks like it runs directly around the middle of the sphere. The seam is not present in any of the other viewports, which view the sphere from different positions. Has anyone else had any problems like this before, who can offer any suggestions? I really can’t think what the cause might be. If code or screenshots would help please email me and I’ll send some… Hope someone can help. Thanks.

You’d better post your code that i can try to recreate your problem and pinpoint where the problem is.