There is nothing "illegal" about the ticket. It is simply priced lower than it would be priced if it were booked by OP, e.g. 2 vs. 1 awards. No different than any other INVOL reroute where it would cost more to book the new ticket than was paid for the old.
AA was free not to offer this reroute, but it did so.
I would not raise it or make a hassle out of it in any way. OP ought to recognize that if he does seek to make a change in any way, the reissue of will be entirely on him and that might mean a second award. So, savor the extra time, but understand that the ticket is effectively wholly inflexible.