all your report are belong to us

As Matt mentioned in his article, beginning with Magic 2014 Core Set, we are changing how the game handles several things, including legendary and Planeswalker uniqueness. The new rule separates the field of play into your battlefield and your opponent's battlefield, and only checks those to make sure that there are not multiple copies of one legend with the same name or Planeswalker with the same type. When multiple copies are on the battlefield under one player's control, that player chooses one to put into the graveyard as a state-based effect until only one remains.
Read the article at WotC's website: Legendary rule change.
Effective on July 13, 2013.