I just watched Minato vs masked man fight and noticed something strange. When Minato hits him with his rasengan, his arm fell apart, but it was the left arm not the right one.
http://www.narutobase.net/manga/Naruto/503/3

From the last chapters we know that Obitos right part of the body is made of Hashiramas DNA.
http://www.narutobase.net/manga/Naruto/603/18

When he tried to hit the rock his arm melted. We see the same thing when he fought Danzo's men.
http://www.narutobase.net/manga/Naruto/475/10

I am not sure if that was a mistake made by Kishimoto, but I think that the one that fought Minato Wasn't Obito, at least not Obito alone.

By the way, this is my first thread, so sorry if someone mentioned this already.