Emissive for static lighting not working if static shadow is off?

I am creating a custom actor for emissive static lighting and I’m quite happy with the result. Yet, I have noticed a strange behavior: in order to have the emissive baked in the lightmass, the mesh must have static shadows on.
Is this intended?

To reproduce this just create a mesh with a strong emissive material, set it to static, turn on Emissive For Static Lighting in the mesh lightmass settings, bake, then turn off the static shadow on the mesh and bake again.
You should notice that without the static shadows the emissive is not considered by the lightmass.

I tried different solutions: setting the material to translucent, using some opacity mask in the lightmass replace, none seems to be working: if the mesh doesn’t cast a static shadow, it won’t feed her emissive to the lightmass.

The only way to achieve what I seek, currently, is using planes so that they are only rendered on the side that won’t receive lighting. Very limitating, still investigating!

Turning on “shadow indirect only” seems to remove at least the main static shadow. Still not an ideal solution but we’re getting closer!