ITEAD: Only gets IP if UART connected during boot

[kdubious]

I've been testing several ITEAD boards, and may have noticed a pattern. Everything worked fine during my initial testing with a Serial USB UART attached.

However, trying to power up these device without the UART attached, they do not get an IP address. In fact, I used Wireshark on my DHCP server, and I see no DHCP traffic unless the device is powered on with the UART connected. Even connecting the UART after boot, and running
$this->bbcode_second_pass_code('', 'ifconfig eth0 down
ifconfig eth0 up')
or
$this->bbcode_second_pass_code('', 'dhcpcd eth0')
has no effect.

I'm using the mainline kernel (4.5) and mainline u-boot.

Do I have a u-boot issue? DTS? Any ideas for how to fix or how to troubleshoot?