After enabling forward shading materials with their decal response set to "normal" have incorrect shading. In the example project there are many pointlights and their specular highlight doesn't display properly.
The licensee explains that the normals passed into the shader are not normalized which is adversely affecting shading.
The decal response "Color Roughness" appears to be working correctly.
The highlights on the material with decal response set to (normal) are significantly dimmer.
The visual appearance of the specular highlights should be the same after enabling forward shading.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-44058 in the post.