@hborre, the problem with what I described as a gamma jump is, I can't show it. Even if I stop the render close to finish, a second later the picture gets brighter. What are you referring to by an OS problem?

My OS is Windows 10 pro, latest build, installed last week, latest updates in place. Graphics cards driver is also fresh from Nvidia Web Side. Could it have something to do with the fact that my PC is nearly 13 years old? At least the CPU and the Mainboard is, other parts are not. I will reinstall Poser 12, to check if I missed this happening there also. Like I said, I only noticed it in Poser 13. Since I use quite a few render engines on the same PC, like cycle's in Blender or VRay in C4D, I think I had noticed if this happens there too.

Any suggestions?