Volume absorption with boolean difference, when smooth shading the cutter?

I'm using a Boolean Difference modifier to cut a cube and a sphere out of a cube.

Then, I've assigned the same material to all objects, and I've removed Surface, and added Volume Absorption:

The sphere and cube that are being cut are set to not show in the viewport:

The resulting object has excessive absorption along the cut surface between the sphere and the cube:

Why is the volume absorption causing absorption along the cut surfaces? How to remove the absorption along the cut surface?

Note:

• the objects are all using the same material
• I've selected the main cube, and done 'recalculate outside normals'.
• I'm using Cycles renderer

Update:

• I also tried applying the modifiers, moving the cutting sphere and cube out of the way, and redoing 'recalculate outside normals' => no change in appearance

Update2:

• screenshot showing I'm using Cycles:

• Also, a screenshot showing a sphere with 'Principled volume', and it is showing as a sphere, correctly:

Update 3:

• hmmmm, wierd, I created the scene from scratch, to log a bug, and it works now :thinking_face:

Note that here are the full steps that I followed, in order to fail to reproduce:

1. Create a new 'General'
2. rename the default cube to 'Main'
3. Click on 'material properties'
4. rename material to 'MyGlass1'
5. under 'surface', click on 'Principled BSDF', and choose 'Remove'
6. unfold 'Volume'
7. click on 'None' , and choose 'Volume absorption'
8. go to 'scene'
9. change 'render engine' to 'Cycles'
10. in 3d viewport, in top right, click on 'viewport shading'
11. Create another object, eg an icosphere, call it eg 'Cutter'
12. go to 'material properties'
13. select 'myglass1' material, to assign MyGlass1 material to Cutter
14. Select Main, go to Modifiers, and add a Boolean modifier
15. select the eye-dropper from the Boolean modifier, and choose Cutter
16. select Cutter
17. go to 'Object properties'
18. unfold 'Visibilty'
19. unselect 'show in viewports' and 'show in renders'
20. Go to 'world properties'
21. Next to 'color', click on the yellow dot
22. choose 'environment texture'
23. choose machine_shop_02_1k.hdr file (from https://polyhaven.com/a/machine_shop_02)
24. Observe that the boundary between Cutter and Main is darkly shaded

Update:

• ah, needs the cutting sphere to be smooth shaded
• so, modified reproduction procedure:

1. Create a new 'General'
2. rename the default cube to 'Main'
3. Click on 'material properties'
4. rename material to 'MyGlass1'
5. under 'surface', click on 'Principled BSDF', and choose 'Remove'
6. unfold 'Volume'
7. click on 'None' , and choose 'Volume absorption'
8. change color to blue, hex 0400FF
9. go to 'scene'
10. change 'render engine' to 'Cycles'
11. in 3d viewport, in top right, click on 'viewport shading'
12. Create an icosphere
13. Rename the iconosphere to 'Cutter'
14. go to 'material properties'
15. select 'myglass1' material, to assign MyGlass1 material to Cutter
16. in the 3d viewport, go to 'Object' menu, and choose 'Shade Smooth' (this is important! With shade flat, things work ok in fact)
17. Select Main, go to Modifiers, and add a Boolean modifier
18. select the eye-dropper from the Boolean modifier, and choose Cutter
19. select Cutter
20. go to 'Object properties'
21. unfold 'Visibilty'
22. unselect 'show in viewports' and 'show in renders'
23. Observe that the boundary between Cutter and Main is darkly shaded

Can also try 'Apply'ing the Boolean modifier, which doesnt affect the result:

1. select Main
2. go to Modifiers
3. Apply the Boolean operator
4. select Cutter
5. go to 'Object properties'
6. select 'show in viewports' and 'show in renders' select Cutter
7. in the 3d viewport, press 'g' for move, and move Cutter away from Main
8. Observe that the boundary between where Cutter was and Main continues to be darkly shaded