Here's the problem. See Panel Here
Itachi says "If you can awaken the Mangekyou Sharingan, then there will be three people who can use it , including myself."
At the time Itachi said this, Kakashi had not awakened his Mangekyou yet. So there must have been one other person besides Itachi and Sasuke, and this has to be Madara as confirmed by Itachi (HERE).
Problem is now there is a fourth User of the Mangekyou (if Saske ever get one) that is Kakashi. Is this an error in the plot, or is Kishi allowing Kakashi's Mangekyou as a wild card?
If you vote neither, please share your ideas why.