Looks like Apple has fixed the symbolic link exploit which allows to access the 1.1.1 rootfs after upgrading.
However, the door has not been fully closed yet ;) Instead of using a symbolic link, just make a hard link (mknod a device) as shown below:
mknod ~/Media/disk0s1 c 14 1
After upgrading from 1.1.1 to 1.1.2, the above hard link still works, and the full system partition can be dumped to a standard DMG, the dumped DMG is mountable on Mac OS X.
