Quote - Just a thought, and maybe completely irrelevant... 

Why is the "Light" showing green in the D3D render settings?
Doesn't this mean there is AO somewhere? AO plus transparency can give some strange shadow artifacts, if I recall correctly.

Edit....  oh, never mind, if it's light-based AO it's ignored anyway.

You are right. I was using a different light set ( i had IDL disabled at the time of the screenshot ) that was using AO on a light. My IDL settings were the same as before, I had just unchecked the IDL in default Render Dialog and switched out my lightset.