I don't know where the uboot bug tracker is so I am posting this here:
How to reproduce:
Using pogoplug E02 with USB flash OS drive inserted, and USB external drive connected (3Tb seagate backup plus, single GPT partition), boot the pogoplug. In my configuration, the 3Tb drive is connected to the first queried USB port.
Expected behavior:
Boots from USB flash OS drive
Observed Behavior:
Hangs at the following stage:
$this->bbcode_second_pass_code('', 'U-Boot 2011.12 (Feb 20 2012 - 21:21:59)
Pogoplug E02
arm-none-linux-gnueabi-gcc (Sourcery G++ Lite 2009q3-67) 4.4.1
GNU ld (Sourcery G++ Lite 2009q3-67) 2.19.51.20090709
Hit any key to stop autoboot: 0
(Re)start USB...
USB: Register 10011 NbrPorts 1
USB EHCI 1.00
scanning bus for devices... 4 USB Device(s) found
scanning bus for storage devices... 2 Storage Device(s) found
Loading file "/rescueme" from usb device 0:1 (usbda1)')
My off-the-cuff guess is that uBoot doesn't handle GPT formatted drives correctly when searching for "rescueme" or doesn't have in-built support for GPT and thus hangs. One workaround idea is to do a check for GPT and refuse to inspect if GPT is found.