Dazzling specular with forward rendering when roughness is 0

Development Rendering
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With forward rendering in UE 4.15.2, setting the Roughness=0 for a material will lead the dazzling specular.

I tested it in a new empty project, which looks much different from deferred rendering, as the pictures below:

Deferred Rendering:

137812-deferred.png
137812-deferred.png1928×1080 376 KB

Forward Rendering:

137813-forward.jpg
137813-forward.jpg1928×1080 325 KB

And it will looks even worse when Metallic is set to 1.

I didn’t meet this issue in UE 4.14.3. So I think it might be a bug in 4.15.2?