Comment 20 for bug 757720

Just an observation,

I ran into the same problem.

I have multiple SATA drives, with Multiple partitions, including NTFS,
EXT3 and Riser. I don't like doing upgrades so I elected to wipe the
existing Ubuntu install.
I ran into the same problem when trying the live installer. I used the
Disk utility to mount the partition I wanted to install on which in my
case was /dev/sda5. After I had the partition mounted I started the
live install and of course it warned me that a partition was mounted
and unmounted it. After that the install proceeded. That seems to have
fixed it.