I tried to do an ftp install of RedHat/Sparc 6.0 from an internal server. When I realized my setup here would not allow the ftp install to work, I tried to backup to the install media selector. When I was at the window for specifying the ftp server and directory the back button appears to have the same functionality as the OK button. Its probably not possible to back up that far in the install process, but this dialog shouldn't have a back button if it doesn't work as a back button.
Was unable to replicate this problem in the final release of Red Hat 6.0 for sparc.