RT does not update wired material colors

[narmer_visual]

When having several materials, which I want to have the same diffuse color, sometimes I use Point3 Controller / Color RGB controller wired into the diffuse color slot. This is better than using VRay color wired into the diffuse map slot, because Point3 controller displays in the viewport, VRay color does not.
When using RT to preview my scene, modifying the color of one material updates all the other materials' in the viewport, but it does not in the RT window. It updates only the one material I was currently modifying, but not the others, which are also wired with the Point3 controller.

Regards,
Gabor