Ever think that maybe someone else took obito's right eye (as a rent) to train it and it was that person that fought minato? Then madara had the person (maybe a zetsu experiment) give the eye back (or he just took it back because the person fail the mission) and thats the reason obito cannot deactivate his sharingon (Well i don't think we ever saw his eye nomal) because it was transplanted back in his eye socket. As we can see in danzo and kakashi a eye that is implanted cannot deactivate, but am not sure about the EMS case..maybe the eye has similar DNA and that is why it can work in someone else (Izuna-->madara Brother/Similar Dna) :shrug: