I, too, have had some vexing results from materials that worked fine in P13.  I've not had the time to dig into it further but I'm thinking the materials for P13 may no longer be reliable in P14.  The problems I have are with materials based on the old Poser root node (so far).  I had made modifications that rendered nicely under P13 but in P14 they render as black... no detail or color or anything.

I'll post more as I have time to look into this... stand by...

Molly