I posted this earlier, but was having troubles sending more info, so here’s an update. I’m attaching a blend file that you can open and run a quick render with to see if similar problems arise (note in the image how the the OSA alpha channel makes a slight halo around the inner sphere; note also in the OSA image how you can actually see THROUGH the outer sphere to the yellow tube behind it). The outer sphere is cut up with procedurally generated alpha mattes, thus I need to use ZTransp in order to see anything behind/inside it (like the inner sphere).
If anyone has a solution to this, I’d be delighted to hear it. Otherwise, I think this is a bug, and for the moment is best treated with some node-editor tweaking…
zTranspAlphaBug.blend (197 KB)