So any 64-bit version will install correctly, regardless of it saying specifically that it is an UEFI iso.
When creating the EUFI installation on a flash drive, are you configuring it as a GPT drive first? Otherwise it will not work. You can use the use the convert gpt command line to do so.
I have no idea why your OS is booting up into the old installation, but if you wish to access the UEFI setup, you can follow the steps below.
dont mind the bullet points, whole format got fucked up when i cp'd the line from microsofts website