Blurry details and dark areas with sharp edges inside clouds

[oggyplanet]

Hi There,

when flying through clouds the noise-details getting blurry and dark areas appear. How to solve this?
Please take a look at the attached files.

Very simple scene-setup, no object-shadows, small view- and shadow-steps...
I'm using max 2009, Afterburn 4.0b, finalrender sp3 with fisheye-camera

Thanks++,
oggyplanet