@ DCArt Fair enough, it was my initial thought also. This was not the case. I'm currendly installing my OS, all drivers and programs again to see whats going on. To have something to compair Poser 13 renders to, I will also install Poser 12.
My guess is, that this behavior originates from the changes inside the Superfly render engine to make it faster wiith less iterations. Some post effects like the denoister or blur could be hard wired to the render engine under the hood, without showing in the actual PostFX Dialog. But thats just me and my opinion. Take it with a huge grain of salt.
Like I wrote above, could be a failior of my graphic card driver, or my old rig that signals that its time has come, I really don't know.