Material seems more glossy when reflecting from skylight

Here is the repo case for Advanced_Lighting

  1. load Advanced_Lighting
  2. change M_Clear_Coat to:
    • BaseColor 1
    • Metallic 1
    • Roughness 0.5
    • Default Lit

Here are my results:

Windows (bootcamp) + NVIDIA 750M

OSX 10.11.6 + NVIDIA 750M

You can see the left most sphere is quite different.
The default material settings in this scene are not easy to distinguish the difference. The issue looks like the roughness is scaled by 0.5