Not sure if this is nUI or something else, as I haven't had a chance to test it yet. I have chat broken down into a couple of tabs: general, guild/party on one toon. I noticed that if I'm looking at the guild/party tab, I can't see the chat edit box — it only shows up when I'm on the general tab. I have no chat mods installed. I do have carbonite, vuh-do, and their info panel plugins. nUI 5.06.26, btw, and everything is as up to date as I can get it.
