To argue that the case in the "shade materials" you should turn off GI and render the scene multiple times without him. If the shade does not change, then the matter is in the GI. Then you go to the section of lessons on 3d visualization and hard read our recommendations for setting V-Ray.
If not, then it is either miracles or bugs version of the software that you use. In miracles we do not believe, and the software can deliver and the other version.