My boyfriend and I had the same exact problem. All he did was put in a ticket with support on the account with the double copies. The GM gave him a code to put in on the other account(or whatever account you would want to put it on it says), while deleting the copy that wasn't supposed to be there.
But I also think, like the person above me, that it would work like Battle.net and allow you to play multiple copies off the same account at the same time.