Running through this process myself I discovered the following in my boot partition at the time of the failure:
16M initrd.img-3.8.0-19-generic 16M initrd.img-3.8.0-19-generic.dpkg-bak 0M initrd.img-3.8.0-19-generic.new
So it seems that the new kernel image is getting created multiple times during the upgrade process.
Running through this process myself I discovered the following in my boot partition at the time of the failure:
16M initrd. img-3.8. 0-19-generic img-3.8. 0-19-generic. dpkg-bak img-3.8. 0-19-generic. new
16M initrd.
0M initrd.
So it seems that the new kernel image is getting created multiple times during the upgrade process.