Post processing stack fog and two camera setup

I have two camera setup. Main Camera renders the world and Weapons Camera renders gun. I usually apply post effects to weapons camera, cause then post effect are applied to guns and world. Unfortunately post processing stack fog in deferred rendering path doesn't work correctly on my weapon camera when "exclude skybox" is checked. It does work fine on my main camera, but I need to use it on my weapon camera. Here's demonstration of the issue: https://youtu.be/a7wdpDIbP9M Unity 5.6p2 Windows 7 Post processing stack 1.02