Hi,
any news about this old bug?
I found a similar (if not the same) behaviour: in a scene with a background, I want to "render select" (or use an include/exclude list) only an object
but it cames up in the render another object, with a glass material, if it has the option "visible in mask" unchecked as in this case;
another way to not have the glass object to appear is to check the "Thin" option so indeed it's related to refraction too.
I attach a sample scene.
Thank you!
Man