No Dynamic Shadows From Stationary Lights in Forward Shading Without Building Lighting

I've observed this issue in 4.18.3 and 4.19.1.
Per Licensee:

So we've spotted an issue that I wanted to put on your radar with dynamic shadowed stationary lights + r.ForwardShading=1

What we're seeing is no dynamic shadows of any kind (no dynamic inset, no CSM etc) being cast from stationary directional lights, until we've done a lighting build. Things to note here:

• This only appears to be happening in forward shading

• We are seeing in-editor preview shadows, it's just in PIE or built games that we're not seeing dynamic shadowing from 'unbuilt' stationary lights.

• After building lighting; CSM, dynamic inset shadows etc then show up in PIE as expected.

• After building lighting and having everything working, then rotating the light seems to invalidate it again and we go back to no dynamic shadows until we rebuild.

Of course we can simply build lighting to get the shadows we're after (this seems to be a persisted state btw, saving the level after building lighting seems to work as expected)

1. In new project, go to Project Settings and enable Forward Rendering. Restart editor.
2. In new level, place basic Cube mesh on floor, set Cube to Movable
3. Add a Directional light, point light, or spot light set to Stationary
4. PIE

Result: Shadows are visible in Editor viewport, but not when PIE.

Expected: Dynamic shadows visible