I have ubuntu 12.04.05 LTS. I've downloaded ubuntu-16.04-desktop-amd64.iso. When I run "Startup Disk Creator" and select ubuntu-16.04-desktop-amd64.iso to write to my usb stick. Then I restart, change my bios to boot from the SANDISK USB. I end up in a live CD of ubuntu 12.04. Which is what I already have. I know I'm running on the usb stick as my desktop is clean and my background image is missing. System Settings Details shows ubuntu 12.04 LTS.
I have used gparted to create partitions on another usb stick, then used dd to copy the iso file to the usb device. Then rebooted, again selecting the SANDISK USB in the bios. And do end up in an ubuntu 16.04 LTS live usb drive. But if I'm having this problem then perhaps others are too?
For some reason it appears that Startup Disk Creator for ubuntu 12.04 doesn't write the selected iso file? Also SDC does not show a version number.
Startup-Disk-Creator works best when running on the same version as the ISO being used. It does not even successfully create a bootable ISO for Ubuntu 16.04 when run on a 14.04 system, so failure on 12.04 is no surprise. The bugs on this behavior are years old, do add yourself to the "does this affect me" lists. As you have discovered, dd is the common workaround, and with perfect media, it works fine.
The problems Startup Disk Creator has result from using some files from a running system instead of just files from the ISO. These files can be the wrong version, and can fail. Another issue the the apparent reliance upon filesystem links, which are in the ISO's iso9660 filesystem, but cannot be used on a FAT filesystem. Just copying the files from the ISO (loop mounted) to the USB (FAT filesystem) misses the "ubuntu" link, and results in a kernel argument reference to "/cdrom/preseed/..." which does not exist. Removing that reference in the grub.cfg will result in a UEFI bootable USB.
The newer mkusb media creator does the dd copy, with more safety features to ensure you select the correct target.