GLSL Textured sphere, odd visible seam

Hey. I’m testing out the following tutorial: http://en.wikibooks.org/wiki/GLSL_Programming/Blender/Textured_Spheres

and it does work, so I tried it on my sky sphere for game use.
Only problem is that I get this weird visible seam which is seen on attached picture on the sphere going upwards.
Any idea what could cause this?


Better visible here on tutorial texture: