I stumbled over another thing where I don't know if it's a bug or if I'm misunderstanding something.
When I insert a Color Correction node in between the normal map (RGB Image) and the Normal socket of the material, its look changes significantly although I did not adjust any settings in the Color Correction node. However if I do the same thing an plug the output of the Color Correction node into the Albedo socket of the material, the result looks unchanged (as it should be). Below is a test scene that shows the effect. In the top row the Color Correction node is places into the Albedo socket, in the bottom row the node is plugged into the Normal socket. You can also see the node layout in the second image. Maybe somebody can solve that problem for me. Cheers.