Fixed - It was indeed a local contact created.
I also had this problem and I fixed it. You guys lead me to it thank you.
My problem was a iMac user with outlook 2011. This person created a local contact for himself and added 3 other people's email addresses to it as additional email addresses. I'm guessing they intended on it being a distribution group but fubar'd that up royally.
So i went into his local contacts, did a search for the suspect email addresses and sure enough the search results returned his contact along with the others that the header was referring to incorrectly.
i then opened his contact he created and deleted the additional email addresses attached to that contact. Problem solved.
figuring this one out was like playing detective work. i registered here just to leave feedback because i could not find much help online about this very strange problem.