1. What happened
Baked light casts shadow for object's back face for CastShadows=On

2. How we can reproduce it using the example you attached
- Open scene 1
- Bake
See that 'Plane (1)' and 'Quad' objects have CastShadows settings in 'On' but they cast shadows on 'Plane' object through their's back faces.
Expected: Such behaviour is expected for CastShadows='Two Sided'. For CastShadows=On there should be no shadows cast through back faces of planes, quads, and other.