Nope, I have only ever logged in at my home network, and I noted that the trade had the lack of a happiness bonus, so I cancelled it and requested to trade. I knew that the school had a global IP, so I told him that only one of us should log in, ever, due to the heavy anti-assist/trade per people on same networks. My friend and I likely do not have the same IP, nor even the same ISP, so I don't see where that could be a problem. We both only joined... 3 days ago, and this is the first time we logged into the school network.
Possibly there's an error somewhere causing trade acceptance/denial messages with one nation will override a current trade, as it only successfully worked when we deleted all our messages. I dunno if this is worth noting or not but it definitely seems like it shouldn't work this way.