The PNG transparency has nothing whatsoever to do with lighting, so it isn't lighting changes.

I'm wondering if your background shader was identical in both. Or if the BG wasn't really black.

Halos are produced even in Poser 7 if you render with anything but a black background color. This is because any partial pixel (where geometry doesn't completely fill the pixel) has to have a partial transparency and a color. The color is a pre-mix of the geometry color and the background color. Since Poser doesn't know why you're making a render, or if you plan to save it as PNG with transparency, it renders the color as a proper blended mix of the geometry color and the background color. So if your background isn't black (numerically 0) then you get some of the render-time background color mixed in.

When planning to do a PNG transparency render, you must render of black or over a BG shader that produces black. This has always been the case.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)