Ok, I was able to reproduce with a very simple project. Create a new project, check "Selectively output to the GBuffer rendertargets in edit:project settings: rendering: optimizations. You’ll need to relaunch to recompile shaders at that point. Then add a cube and stretch it out so it casts a big shadow. Put a smaller cube completely within the shadow. Rebuild lighting. The smaller cube will be getting light instead of being in shadow.
Here’s a picture:
