Board Thread:Naruto Discussions/@comment-25100062-20140813144247/@comment-1705651-20140814013258

My guess is Obito can only grant his Mangekyo during the ghostly possession, once the fight ends he will interrupt his connection with Kakashi to go back to Rin and his new pair of Sharingan will disappear as a result. Obito said it would be temporary after all.