at this point it is to say taht i am not sure if this is really a bug or i am just too stupid :D
take a look at my log.txt:
Done 10596200.000000 mutations (34.492839 mutations per pixel)
Time elapsed: 7m, 33s
Mutations per second: 23366.790819
average_im_pixel_f: 88.528564
sum_F: 27195974.097018
scale_factor: 0.033628
img_av_i: 2.977062
Y_white: 52.603523
recip_Y_white2: 0.000361
------------------------------------------------
//this is the point where the render window turns white
Done 10707100.000000 mutations (34.853841 mutations per pixel)
Time elapsed: 7m, 38s
Mutations per second: 23369.830552
average_im_pixel_f: 89.426910
sum_F: 27471947.720748
scale_factor: 1.#INF00
img_av_i: 1.#INF00
bidirectional =true
MLT =true
i guess it might have sth to with the rgb_absorptivity of one of my materials, since evereything worked before i played around with it. but: it could be anything else ^^
if you want to ask me sth else about my settings, go ahead.