Why does Ubuntu 12.10 Beta2 insist on commiting changes to the partition table even as no real changes has been done?

This is a show stopper for me as I'm installing without a CD/DVD ROM.

This is how I go about it.

I downloaded the iso image and extracted vmlinuz and initrd.lz to the same folder I keep the iso image. Configured grub (0.9x) to boot /ubuntu/vmlinuz with the iso image like this:

title ubuntu live-cd
kernel /ubuntu/vmlinuz boot=casper iso-scan/filename=/ubuntu/ubuntu-12.10-beta2-desktop-i386.iso ro quiet splash
initrd /ubuntu/initrd.lz
boot

This works well and I get a running livecd session. The iso image is mounted on /isomedia (or something similar).

The spare HD space where I want to install Ubuntu is in the logical area (at the wery end of the disk). I have tried both to use the space as empty and preformated with ext4.

After selecting the partition and selecting "use as ext4" and selecting a mountpoint (/) I get the message: "The installer needs to commit changes to partition tables, but cannot do so because partitions on the following mount points could not be unmounted" "/isomedia" (or something similar).

Is this a "feature" of the installer? To insist that everything is unmounted even if no changes is nescesary (as fare as I understand). It's probably a safety feature but is it needed? I have cahnged layouts with parted and gparted (at the end of the disk) for years without any failures.

I understand that booting the iso image like this is not the common way. But it is just such a beautifull way of doing it when you hav a running system and want to play with another.

Any one had any success installing Ubuntu (12.10 beta2 ) like this?

Best regards Uten