I think the way it's supposed to be is that tank is party1, healer is party2 and so on. As far as I can tell, this is broken in current WoW. Now that I mention it, I think I saw the same problem before I started using nUI. Sigh - if this worked the way Blizzard says it does I could get rid of LiteAssist. My other option is to set focus on the tank, but that clobbers my minimap. I'll just have to wait for nUI 6 I suppose