Linux Mint Mate
Blender 2.81 Alpha
Discovered while trying to catch shadows from volumes on surfaces for compositing.
Surfaces inside of volume meshes are not shaded (lit/shadowed) by the volume if the volume is invisible to camera rays
(checkbox in Object Properties -> Visibility -> Ray Visibility -> Camera)
As far as i can tell this also affects Holdout.
Current workaround: make sure volume IS visible to camera rays, and instead bypass it in the volume shader using the Camera Ray socket on the Light Path node
Open attached .blend , press render
Note the missing shadow/light where the volume cubes intersect the default cube.
I have in the .blend also included the "expected behaviour" by using the workaround, switch the Scene from "Bug" to "Workaround" and press render again.
Note the shadow/light now covers the default cube properly.