That's not a GSX bug, of course. It's a limitation of the P3D graphic engine, that doesn't support the concept of polygon meshes that can block either shadows or dynamic lighting. For example, if you place a dynamic light on the 2nd floor of a building, it will lit the 1st floor too, and up to the ground.
If we flagged the passengers to not cast shadows, they will never cast shadows, even when they should, for example when walking on the apron so, users would see that as a GSX bug to. Either way, we can't really fix it within the limitations of the sim graphic engine.