The Bokeh Blur node produces black images when the bokeh size is small and the catadioptric effect is being used. According to Sergey that leads to a situation where the blur has to figure out pixels with 3x3 area surrounding (or something like that), and without enough precision that process fails because it has to differentiate between the black dot in center and the black surrounding.
The weird thing is that this doesn't happen if you enable OpenCL. Turning down catadioptric to zero fixes that, but of course that's not ideal.
See attached blendfile.


r49281
OSX / Ubuntu