Quote - I haven't been able to reproduce your issue, moriador, although my largest render was 3000px. Will try a bigger one, but in case I'm missing something, this is what I've got in my scene and render setup:

SCENE ELEMENTS

BB's EnvSphere

1 - one sided square primitive set to 3 ambient.

1 - displaced ball primitive with SSS applied.

(2 lights with diffuse and specular set to black)

RENDER SETTINGS

I haven't delved into D3D's advanced render Firefly GUI. In the regular render settings:

Casts shadows, SSS, Raytracing all checked; Use displacement on.

Raytrace bounces: 1

IC: 50

Indirect Light: Quality: 10

Pixel samples: 4

Min shading rate: 0.4

Min discplacement bounds: 0

Gamma correction: 2.20

Post filter: box / 1

Am I missing anything?

No lights in my scene. Turn yours off? Also, I've been rendering with indirect light quality of at least 50. Below that, there's too much mottling from the emitters to be any use in a real scene anyway. With the primitive, I'm seeing the artifact even on smaller renders.

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PoserPro 2014, PS CS5.5 Ext, Nikon D300. Win 8, i7-4770 @ 3.4 GHz, AMD Radeon 8570, 12 GB RAM.