Hello!
When joining geometries (ctrl+J), if one of them already has a material, after joining them VRay creates an empty slot, which is a bug.
To reproduce it: add an object to the scene (e.g. cube), create a new material for this object, then add a new cube and join them. The new slot will appear.
Are you sure it’s V-Ray that is doing this? We don’t have any code that adds material slots and it seems to work the same way with V-Ray disabled. Could this have been changed in Blender in recent versions?
You’re right. I noticed it yesterday while vray was enabled, but somehow it didn’t happen when I switched to cycles. I tested it today again and seems to be a blender thing.
Thanks for checking. Should I keep the post or delete it?
No problem, no need to delete the post 