Hi,
by case I tried to install F25 Beta in legacy mode on an 64GB flash medium. And surprise it works.
This means Anaconda problem when installing F25 on an USB flash medium in EFI mode,
but in Legacy mode ok. I run an Acer laptop with Win 8.1 on the internal disk.
I think this is good news to find a way to solve this EFI - Anaconda problem.
Kind regards