Comment 3 for bug 1184636

ubuntu does not use live-build for bootable images, only to create rootfs'es ...

bootability happens from the debian-cd wrapper that uses the rootfs created by live-build (netboot is even completely created by debian-cd from a debian-installer build) unless the complete infrastrucure ubuntu uses to build images gets changed to not use debian-cd for this step, i doubt there is big interest in adding such functionality to live-build ... (patches accepted as usual indeed)