I had some discussion with Ondra about this. Basically, the problem is inherent to any HDR renderer and all of them either show aliased high contrast lines or somehow "fake" it so that they are not so visible.
The problem is that Corona internally has float HDR values that are practically unlimited. So even after exposure transformation, most of the pixels will have a value between 0 and 1 (let's suppose a greyscale image just for the simlicity's sake), but there will be a few super-bright pixels - highlights. These typically appear in specular highlight points or if you look directly into a light object. Now, let's say that these pixels have a value of 1000 and you are doing anti-aliasing on the border between this light and pitch-black background. No matter how many samples you do, your averaged antialiasing values will be mostly higher than 1, which makes them white in the final image. So while the antialiasing is perfect in the original data, it looks jaggy in the transformed image.
The way to fix this is either get rid of the high values - this is what highlight clamping and compression does - or apply some postprocessing to the image. You can either try bloom and glare (after all, looking into such a bright object will produce such effects either in a camera or in your eyes) or the sharpening/blurring post-effect. Look at the attached image to see how it worked for me in a simple scene.
Hope this helps you :-)
