Just found a strange behavior of a displacement map (carpet):
1. Using a Vray sun and Vray-Camera, the displaced carpet displays a strange shadow-edge at the transition to the GI-lit area. It is somehow connected to the Size-Value of the sun, since big size-multipliers result in horrible transitions …
2. Strangely the sunny part of the carpet displays much darker shadow-areas than the pure GI-lit area. While the Gi-area looks nice and soft bluish, the sunlit area has extremely harsh contrasts, which are partly darker than the GI-area, which looks very strange.
So this is because of the Oren-Nayar-Blinn shader on the carpet; if you replace this with a regular Blinn shader, or with diffuse VRayMtl, it will render fine.