Currently I have Arch Linux installed as my primary OS, and wish to install Windows 8.1 as a secondary so I may utilize certain special hardware (a capture card which has no Linux drivers at the moment) without abandoning my main OS.
I have an EFI partition formatted as FAT32 as my first partition, which is mounted in Arch as /boot and is where GRUB and the proper EFI boot files are installed. There is 477MB of free space on that partition, so I would imagine Windows 8.1 would be able to reuse that partition to store its own EFI files, and simply register a new entry with the UEFI firmware.
Regardless of whether it does reuse that partition or not, I have ~750GB of unallocated space on my hard drive which I will be giving to Windows 8.1. When I go to install Windows 8.1 to this unallocated space, I enter my product key, select custom installation, then select the unallocated space to install Windows to. It begins installation briefly, but then an error pops up claiming that my EFI partition is formatted as NTFS. This is false, I know for a fact that it is formatted as FAT32.
A quick google search suggested that perhaps the USB installation medium I am using is formatted as NTFS, so I double checked that and it is indeed formatted as FAT32. I have no idea what I am doing wrong or why it thinks my EFI partition is formatted as FAT32 when it is not.
EDIT: Here is the output of gdisk, as requested
gdisk -l /dev/sda
GPT fdisk (gdisk) version 0.8.10
Partition table scan:
MBR: protective
BSD: not present
APM: not present
GPT: present
Found valid GPT with protective MBR; using GPT.
Disk /dev/sda: 3907029168 sectors, 1.8 TiB
Logical sector size: 512 bytes
Disk identifier (GUID): EB7B1BE6-5D74-44D9-81FD-616FCC19F20C
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 3907029134
Partitions will be aligned on 2048-sector boundaries
Total free space is 1674610797 sectors (798.5 GiB)
Number Start (sector) End (sector) Size Code Name
1 2048 1050623 512.0 MiB EF00 EFI System
2 1050624 68159487 32.0 GiB 8300 Linux filesystem
3 68159488 135268351 32.0 GiB 8300 Linux filesystem
4 135268352 2232420351 1000.0 GiB 8300 Linux filesystem
It does not output the filesystems. If you want that, here is a screenshot of GParted's results for /dev/sda
gdisk -l /dev/sda
to make sure?