As I had this issue too I read somewhere that somebody solved it by removing his iPod from the USB port. So I went through the installation process and when it hung I aquired a shell and killed all partman processes. Then removed the USB stick which contains the Debian CD. I went to "Partition disks" again and it complained the "CD Rom" was missing. I clicked "no" twice and finally got the option to partition manually.
That was a success. But the next step to install the base system failed as the CD Rom was gone. Mounting via shell didn't work, so I issued a "udevadm trigger" and went to the point to mount the install medium again. From there the installation went through. So it seems the installer has problems with USB devices which are "disk volumes". -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org