Carlos Terrera has been disqualified for deck stacking. At the beginning of round 9, he brought a "preshuffled" deck to the table and presented it to his opponent for a cut without shuffling at all. Further inspection of the deck revealed that it was evenly distributed between lands and spells, with no lands next to each other and no more than two spells next to each other.
"Terrera admitted to performing a 'mana weave' on his deck," head judge Collin Jackson explained. "He was apparently unaware that mana weaving is illegal unless it is followed up by a random method of shuffling, such as riffle shuffling."
Not only is presenting an unrandomized deck to an opponent illegal, at high-level events such as this it necessarily earns a disqualification. Deck stacking is deck stacking, no matter the player's intent. Jackson stressed that it is the responsibility of the player to know and understand the rules.
Jackson's statement continues: "At this level of event, players are responsible for knowing the rules. The Universal Tournament Rules clearly states that players must present a random deck to their opponents, and Terrera failed spectacularly in this respect. Terrera was very cooperative and honest in our investigation, but nevertheless deck stacking is a very serious offense that should never be treated lightly. Terrera's shuffling method makes it very unlikely that he will experience mana problems and thus it gives him an unfair advantage over his opponents. I explained the shuffling rules to Terrera and I expect that he will pay more careful attention to them in the future."
Terrera, a native of Argentina, held a 5-3 record before the ruling.