strange stains with the volume material

[parcher]

Hi,
I noticed a strange effect using the volume material.
I have created a sphere and the surface divided into two parts. In image 1, I applied to both surfaces of the same volume material, obtaining a correct result. In image 2 I applied to surfaces the material volume and a copy of it, getting an incorrect result.

Can any of you explain it?
Thank you

[maru]

Hi, any chance to get a scene where this happens? I think it could greatly help our developers.

[parcher]

Hi maru,
I enclose a test scene. I use the A6 RC3.

Thanks

[maru]

My guess is that this is because of refraction. The object is treated as one when using one material - light hits the same object/material, then travels inside one object/material, then exits. When using two materials, they are treated as separate objects/materials, so it's basically just like using two non-solid objects with refraction - which is incorrect.

This is an explanation from me, but I'm interested what our developers would say here.