Plenty of 500 Internal Server Error - no implicit conversion of Fixnum into String

I noticed a lot of these in the log; the site does seem to work otherwise though. Should I be worried? This is on 1.3.2.

Started GET "/t/opensuse-package-for-syncthing/189?page=2" for 207.46.13.139 at 2015-06-15 07:58:55 +0000
Processing by TopicsController#show as */*
  Parameters: {"page"=>"2", "slug"=>"opensuse-package-for-syncthing", "topic_id"=>"189"}
Completed 500 Internal Server Error in 25ms (ActiveRecord: 7.1ms)

TypeError (no implicit conversion of Fixnum into String):
  app/serializers/post_stream_serializer_mixin.rb:28:in `block in posts'
  app/serializers/post_stream_serializer_mixin.rb:21:in `posts'
  app/serializers/post_stream_serializer_mixin.rb:11:in `post_stream'
  app/controllers/topics_controller.rb:485:in `block (2 levels) in perform_show_response'
  app/controllers/topics_controller.rb:482:in `perform_show_response'
  app/controllers/topics_controller.rb:82:in `show'
  lib/middleware/anonymous_cache.rb:121:in `call'
  config/initializers/quiet_logger.rb:10:in `call_with_quiet_assets'
  config/initializers/silence_logger.rb:26:in `call'
  lib/middleware/request_tracker.rb:70:in `call'
  lib/scheduler/defer.rb:85:in `process_client'
  lib/middleware/unicorn_oobgc.rb:95:in `process_client'

This seems to have been caused by trying to use the solved plugin 1.3.2 - I don’t see these in the log any more after re-bootstrapping without that plugin.