Can somebody take a look at the discussion here: https://github.com/rails/rails/pull/12607 (suggested fix at the bottom) tl;dr: there''s an obscure race condition which only happens when two threads dispatch into method_missing on instances of the same ActiveRecord model. The net result is that one of them successfully generates + calls the requested method while the other fails with NoMethodError. :( The fix is (as far as I can tell) pretty straightforward, so this would be great to get into 4.0.1. --Matt Jones -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Core" group. To unsubscribe from this group and stop receiving emails from it, send an email to rubyonrails-core+unsubscribe@googlegroups.com. To post to this group, send email to rubyonrails-core@googlegroups.com. Visit this group at http://groups.google.com/group/rubyonrails-core. For more options, visit https://groups.google.com/groups/opt_out.