GRUB can't read FAT file system

[SevenBits]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Hello,

I've been having a rather strange problem with GRUB, one that I have
been encountering for a while. For some reason, GRUB cannot read
partitioned FAT file systems on my, as well as others', USB drives.
This occurs on all GRUB releases I have tried, including the
development version through git.

I have a standalone GRUB for EFI image that I generated with the
grub-mkimage tool as follows. Notice that I have included the FAT
module as part as PART_FAT:

../grub-mkimage -d . --format x86_64-efi --config
'/home/username/Desktop/grub.cfg' -o ~/Desktop/boot.efi boot linux
ext2 normal configfile lspci ls loadenv help echo fat exfat multiboot
multiboot2 terminal sleep loopback normal fixvideo iso9660 loadbios

When I boot into GRUB and go into the normal prompt, trying to list
list devices works, as I'll type verbatim here:

grub> ls
(hd0) (hd1) (cd0)

Typing the following should work, but doesn't.

grub> ls (hd0)/
error: unknown filesystem.

I know that (hd0) is the identifier for my USB drive, because the
access indicator light flashes while that operation is being performed.

Now, if I format the USB drive to have a FAT filesystem but no
partitions, the operation works. For instance, this command:

 sudo mkfs.vfat -I /dev/sdX -n LINUX

produces a drive that functions as expected.

This has happened not just to me, but to others that are using my
compiled GRUB image as well. So I don't know if this is an issue with
GRUB or something that I'm doing wrong. I've made dumb mistakes
before, so this is a possibility. Any ideas any one has would be
appreciated.

- -- SevenBits
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.14 (GNU/Linux)
Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/

iQEcBAEBAgAGBQJSpL6NAAoJEFbRvtGxmFPEFEMIAMEgXSJldLiy2ljTytVfKeUE
2pQAMxEIGboYEzzhu2UX4znQmn0CI6vsutb4buDjxy5Z2aBS6AB7JL5BqpR0yK/I
WKOElwbG0HYB1D3KEcXetLXS/1z4/OQIqw7Vme5zcqrLjLF8YqNSR3EAhASkDR3o
x5SEneGSVDEvSsiUxfFaMkfO6LyZlbs0oDQMnO9bkBsfig3F/sqjug7gNbcN6LJY
tvher2r3SE22kF6mNfjoiEPPuyVJ5UfMamrMOT4A0T2w2ohCH5LUf5bnrZ3/WAti
h1knsei/P5hQ2SGQ1If/O2nvOTfXh27m4N/5XTgecsDYuMdEJbtpe8CwVX9tifE=
=sKnK
-----END PGP SIGNATURE-----