In line 342 of Sphere.java, a fixed texture delta is introduced:
         float textureDelta = 1.f / 256;

I am not sure whether such delta is necessary at all, instead of using the exact ends of 0.0 or 1.0 for the texture mapping at the poles of the sphere?

At least for higher divisions than the default divisions of 64, e.g. 512, that fixed textureDelta would be too big and lead to wrong results.