I have the following line in my ActiveRecord model:
class Record < ActiveRecord::Base
has_many :users, :through => :record_users, :uniq => true,
I ran into something similar before and I believe it's an AR bug related to PGSQL (https://rails.lighthouseapp.com/projects/8994/tickets/1711-has-many-through-association-with-order-causes-a-sql-error-with-postgresql).
I got around it by dropping the DISTINCT (:uniq) directive and resolved the uniq records another way. Kind of a bummer though.