I'd love to see Corona work a bit more like V-Ray when it comes to allowing certain types of objects be transparent to refraction/opacity, so that things like this don't happen, making finely controlled compositing impossible with corona (without resorting to multipasses which is a pain) :)
Zdepth+Mattes+AmbOcc+all Corona Essential Passes should be able to be configurable to be seen through refraction, thin glass & opacity maps for flexible compositing.
I think this would produce a much more solid working experience especially if you're coming from the old school pass rendering systems like vray, mental ray, final render, renderman, among others.