The event has always had a rule on the number of tickets an individual person is allowed to purchase. Preventing people from buying tickets in bulk to sell at exorbitant prices later, scalping, is the main reason for this practice, but it is not a restriction the people behind PAX have done much to actively enforce.
This year Robert Khoo, Penny Arcade business manager, personally went through the ticket sales to try and isolate cases where people were using multiple accounts to purchase more than the limit of tickets. Once he had isolated the most blatant cases, the worst of which was one person who was able to order 300 tickets, he issued a refund on those worst cases. The tickets in question will go back on sale at an unspecified future date.
Khoo confirmed that less than one percent of the ticket orders were affected by the refunds. For those of you who missed your chance to pick up tickets, keep your eyes open for the upcoming sale of them. They are likely to go almost instantly, as fast as the total number of tickets went.