Active Record habtm joins bug

I'm having some problems with joining in a habtm association.

class Document < ActiveRecord::Base
  has_and_belongs_to_many :customers, :uniq => true
end

class Customer < ActiveRecord::Base
  has_and_belongs_to_many :documents, :uniq => true
end

Document.joins(:customers).first

results in

ActiveRecord::StatementInvalid: PGError: ERROR:  invalid input syntax for type boolean: "customers_documents"
: SELECT "documents".* FROM "documents" INNER JOIN "customers_documents" ON 'customers_documents' AND "customers_documents" AND 'document_id' AND "customers_documents"."document_id" AND 0 AND "documents" AND 'id' AND "documents"."id" AND "customers_documents"."document_id" = "documents"."id" INNER JOIN "customers" ON 0 AND "customers" AND 'id' AND "customers"."id" AND 0 AND "customers_documents" AND 'customer_id' AND "customers_documents"."customer_id" AND "customers"."id" = "customers_documents"."customer_id" LIMIT 1

As you can see it adds quite a few weird join conditions:

ON 'customers_documents' AND "customers_documents" AND 'document_id' AND...

Also:

AND 0 AND