The Opacity and RTP seem to be bugged. What's previewable in RTP doesn't even exist in the render. And when you harden the colour what does finally show is not what the result is.
It's almost as if the RTP can process the opacity like it should in render, but not the render engine. Cause I'm assuming the hard edges are the hard falloff of simple shapes that doesn't actually transition to 0 smoothly like i've been talking about.