Board Thread:Theories and Speculation/@comment-30303455-20161023144410/@comment-25122992-20161023145348

Read the trivia section of the Kamui] article. On several ocasions, Obito was shown using it with normal Sharingan. Can be just an error, but most likely was done in order to avoid spoiling Obito's Mangekyo and thus his true identity when it still wasn't revealed.