I've come across the problem.
I'm trying to boot a bootable SD Card using UEFI.
However, this doesn't work, as there is no "SD Card" boot option AFAIK.
I have tried putting all the USB-related options before the hard disk in the boot order.
I know the SD Card is bootable because it can boot through changing UEFI to Legacy, and booting either from "USB Key" or "USB CD/DVD"
However, I can't use Legacy in order to install the OS on the SD card, as it would mess with the MBR and render my UEFI Windows 8 broken or corrupted (or so I am told).
I've also tried disabling Secure Boot Mode and using a SD-to-USB adapter (which I will try using again, there may have been a driver problem).
If you need any more info, I'll try and give it to you.
Thanks!