I've rendered a scene with aiAtmosphereVolume and 3 lights. While it looks fine either with arnold render view or ipr when i render it to disk i can't see the background i.e. the sky (exr output). When saving multi-channel exr or jpg through arnold render view it works fine, but saving other formats such as tif or png leaves the sky out. Two sample images (jpg with the background) and png (with no background) attached.