Mobile Shader couldn't use Cubemap of SkyLight?

When i switch “Preview Rendering Level” to mobile(no matter High-End Mobile or Mobile/HTML5),the material has began to lose the reflection from Skylight’s cubemap in the scene.

Then i dive into UE source code of the rendering part,i found that it seems that the mobile shader(MobileBasePassPixelShader.usf, etc) doesn’t take cubemap into specular calculations.

So in order to add cubemap calculation on mobile, do i have to change the mobile rendering pipeline in C++, or i just miss some configurations/settings of the engine?