When I render images with premultiply off in imager node renders with multipass MB don't look good, they pick up black background color in the blurred areas. With premultiply on renders look fine. Please see attached images.
A side effect of average the rendered images perhaps? ... I am not sure at all about what could be the problem. Anyway as I said before, I hope to see soon native motion blur in Octane to deprecate the multipass MB code
Computer Graphics Software Developer Octane plugin development and support: LightWave and Houdini