I created some more riders and encountered another problem, that was mentioned before some time ago I guess.
The rider here is partially lit by the sun. The shadow looks jagged and nasty. I didn't notice that before, but in my original image you can see something similar on the forehead of the horse.
Switching off smooth normals produces smooth shadows, but of course the model looks a bit facetted.
I searched the forum, but couldn't find a solution. I played with all settings in the render subdivision settings, tried displacement vs. raytrace, switched off displacement entirely, nothing solved the problem.
Is this a known error, or is there a workaround?