Comment 3 for bug 1372953

I repeated this test to be sure it wasn't a fluke or an error on my part and it was easily reproduced. Just select a partition with a pre-existing Ubuntu family install (in this case it was a simple pre-existing / with only an assigned swap - no /boot or /home) then keep the existing size, select ext 4, select format, and select / as the mount point.

No formatting even begins because I'm still able to boot the pre-existing OS after aborting the install process. I'll repeat ASAP with an Ubuntu iso to see if this is limited to Ubuntu GNOME or not.