On the image below you can see two identical spheres with same size/material/lighting conditions but with different visual results of lighting. Both was modelled in IrrEdit with several clicks.
The difference between these spheres is how their size was obtained.
Left sphere is of radius 500 and of scale (0.01 0.01 0.01)
Right sphere is of radius 0.5 and of scale (10 10 10)
Maybe problem is caused by normals' scaling, I'm not sure.