Can't Manually Assign IP in v374.42, N66U

[WiFied]

When I look in Network Map -> Client Status, I see two different IP addresses for the same MAC address.

When I look in Syslog -> DHCP leases, I see the correct two MAC addresses being logged for the two IP addresses.

I am trying to assign different manual IP addresses to each of the MAC addresses, but when I try to do this in LAN -> DHCP Server, it sees one MAC address that has been given two different IP addresses, so it will not let me assign a second IP address to the second machine.

My network:
N66U - EAN66 adaptor - Linksys switch - 2 devices

(devices: GBox MX2 and Dune HD player - the MAC address from the Dune player is the one that is getting assigned to the GBox MX2)

Thanks for any advice on this. I have unplugged, reset, and connected the network with only the GBox MX2 connected, but the incorrect MAC address is still assigned to the Gbox MX2.

UPDATE: I was able to copy the correct MAC address from Syslog -> DHCP leases, pasting it into LAN -> DHCP Server, and now the manual IP address assignment works. But, when I look in Network Map -> Client Status, I still see two different IP addresses for the same MAC address. Something's not right, but it's working.