For the final part of issue #50 of "MLP: FIM", I got a theory.
Starlight and Celestia orchestrated it. Celestia removed the Elements of Harmony from the tree but knew they won't work on Accord due to him being absolute order, and knew that the attempt would backfire and would turn her and the rest of the Mane Five into brainwashed ponies.
But Celestia was counting on that as she knew Accord would drop his guard, thinking he has won. She knew Starlight would find a way to convince Accord to come to his senses...and that gambit worked! Accord released the ponies from his control and Discord return.
What do you guys think?