So, how do I make it skip that halo? I see there is a len(sphere._grids) == 0 test, but this case there are two grids so it passes that.
I think the problem might be with the bounds. If no points within the sphere satisfy the radius bounds, it will fail. I will commit the changes in that patch I sent you and then we can insert a try/except block for the exception I added; that is the pragmatic solution, I think. But I really, *really* think we need to figure out why the radius bounds are not giving us any points.
-Matt