When rendering a mesh with subsurf activated a random number of black cells appear. It looks as if a mesh were superimposed to the subsurfed with its normals inverted, so you can see it here and there as a black wireframe.
It can be solved sometimes by increasing the level of subsurf or (obviously) by switching off the subsurf at all. (Or switching to 2.27

I've heard of other people at the hispanic community at nicodigital having the same problem, both linux and windows.
Any other suffering soul here ?
(I'll upload a screenshot soon).
Cheers.
malefico.