has_many : << method doesn't handle :conditions

class User < ActiveRecord::Base
  # Follow topics
  has_many :subscriptions
  has_many :bookmarks,     :through => :subscriptions, :source => :topic, :conditions => "subscriptions.notification = 'f'"
  has_many :notifications, :through => :subscriptions, :source => :topic, :conditions => "subscriptions.notification = 't'"
end

john.notifications << some_topic

INSERT INTO "subscriptions" ("topic_id", "notification", "user_id") VALUES(361323, NULL, 1638)

Expected sql would be:

INSERT INTO "subscriptions" ("topic_id", "notification", "user_id") VALUES(361323, "t", 1638)

( "t" for postgresql true boolean)