Ever since H15 came out I've been facing a problem with how Principled shader's metallic channel is represented in the OpenGL viewport. When I assign a metallic map to it, and set the metallic slider to 1, the OpenGL shader shows the whole surface as 100% metallic. Of course Mantra renders it out correctly.
I couldn't find any information about this phenomenon. Is it a known issue? Are there any workarounds?

The viewport's GLSL shader is an approximation of the Principled shader, and as of 15.5, doesn't support metallic texturing.

Thank you for your response, @Twod. Is fixing this issue on SESI's plan for the near future?

Yes, but not for 15.5.

twod
Yes, but not for 15.5.

These are good news. It's a little bit troublesome having to unlink a texture referenced by a metallic channel to get a decent preview in the viewport.