
Using a higher resolution sphere does make the artifacts smaller (obviously), but for an HD 1080p render the sphere would need maybe 100,000 triangles for the artifacts to become small enough not to be a problem. Seems "a little" excessive, especially considering graphics card RAM limitations.
I know this is beta software, and I'm perfectly fine with some bugs as long as they will eventually be sorted out. Since Mental Ray and 3Delight don't have this problem (these are the ones I've tried) there is obviously a way to deal with the issue on the renderer side.