Mint-14 install from ISO file stalled for unmount

[LenWeisberg]

An ISO-based install attempt failed on an unexpected and failed
attempt to unmount the ISO device.

I successfully booted from a Mint-14 ISO-file,
    linuxmint-14.1-cinnamon-dvd-64bit.iso
The install started fine, but I soon got this 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: /isodevice
> Please close any applications using these mount points.
> Would you like the installer to try to unmount these partitions again?
There were two buttons: [goback] [continue]
      and also an [x] in the upper right corner of the message window.
With all choices it just sat there, and I had to hit the power button.
I tried again with the same result.

This is especially surprising since my ISO file is on a completely separate
hard disk from where the installation was being done, so I wouldn't expect
its partition table should possibly be changed here.
It seems that the logic here is simplistic and/or overly cautious.
The dialog logic also seems to be confused.

Last system I installed was Ubuntu 10.04 and I am quite sure that
it worked fine from an ISO file, with essentially the same menu entry.

For more completeness, here's my Grub2 menu entry:
menuentry "> ISO Mint-14.1 Cinnamon - Nadia - ISO (sdb6) <" {
   search --no-floppy --set=isodisk --label data2
   set isofile="/iso/linuxmint-14.1-cinnamon-dvd-64bit.iso"
   loopback loop ($isodisk)$isofile
   linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile noprompt
   initrd (loop)/casper/initrd.lz
}

Of course, this is not a show-stopper since I was able to install from DVD,
but I would much rather use a hard-disk if possible, because it is so fast
and convenient compared to using a DVD.