I just had a look at PD Claudia.

I don't get the shader for the EyeSurface: In her P9 shaders she has - for some reason - set the EyeSurface material to a strange setting. She has a black simple color node (which is 0 as far as I know) connected to the transparency channel which is set at 1. This results in a non transparent surface for the preview. It renders transparent however - that is a complete mystery to me.

So, disconnect the black Simple color node from the transparency node and leave the rest and as far I can see it renders the same - but I may be mistaken here since I don't understand what the black Simple Color node is doing

For those who are curious: Simple Color connected to transparency (Set to 1), Trasparency Edge (set to 1) and Transparency Falloff (set to 0). Diffuse, spec and all the rest set to 0. It renders as transparent and preview is black

Adam35: Check the other figures if there is something similar going on