Interesting. Seems like it only occurs when using full HDR rendering. I'll look at it sometime later, but I don't know when since I've been busier lately.

Ok so the way this effect works is that during rendering, the background is replaced with a specific shade of green, and then during post processing that shade of green is replaced with the desired color (in this case red) and everything else is replaced with a different color (in this case black). However, full HDR rendering alters colors through its own post processing/tone mapping, so the shade of green will not be exactly the same, so everything is instead replaced with black. I'm not sure this can be fixed without some very ugly hacks.

Not trying to come off pushy, is there any idea of this being patched even if with some ugly hacks? Full HDR rendering is just amazing and I love using it

There’s an option to disable HDR rendering during boss fights, but a full fix is unlikely.