Quote - Here's a Global Radiosity atmosphere where the defect is even more obvious.

Paloth, I loaded one of Vue 6's GR atmospheres to see how it handled a similar GR atmosphere. (I like the darkened area under your sphere better than mine!) :p

When I first saw your render, I didn't t perceive anything defective; I would expect such a prominent  shadow, as the sun is facing the sphere. But yah, I'm no expert! :p

I like the wonderful light-bounces affecting the back of your sphere, btw.
Mine looks like the dark side of the moon! ;)