You have to boot the DVD in the UEFI mode. If you have an F key to give you a boot device menu, use that. If not, go into the bios and select the UEFI DVD entry.
Did you install Ubuntu as UEFI?
But a GPT drive has a hidden partition, which you say it created earlier. If the drive is already GPT, it does not need to be recreated. It might only create a EFI and OS.I tried several different ways to show only 2 partitions, but even when I preset the drive to GPT, it still showed a 100 MB, 128 MB, and OS.
UEFI can install like MBR in that it may use a single EFI partition for both UEFI installs. So installing with one drive disconnected might be beneficial, but your choice