Normal mapping on static objects acting weirdly with single mixed directional light

Hello,

I have a scene with one single directional light only. The light is set to 'Mixed' mode so that it bakes lighting on static objects on editor time and illuminates non-static objects in real-time.

Everything works beautifully, except for the normal mapping on the static objects. Normal maps are simply ignored until I add one more directional light that is set to real-time.

Is this by design? I can always change the mixed light to be baked and then add the real-time light. But I am curious as to why is this happening.

Also, is this 'mixed' mode normal mapping behavior going to change in the Unity 5.6 version with the 'stationary' light mode?

It would be nice for me to understand the whole thing just a little bit more.

Thanks,
Stepan