to_json not working because reflections are wrong

I have a class called "Foo" that looks like this:

class Foo < ActiveRecord::Base   belongs_to othermodel end

and a class "Bar" that looks like this:

class Bar < Foo    belongs_to thirdmodel end

When i try to serialize bar with : bar.first.to_json(:include => :othermodel), it fails in production mode. Strangely it works in the development environment. I digged around and found that the bar.first.class.reflections.keys only includes "thirdmodel" and not "othermodel" in production mode.

I can't explain that, in rails 2 and in the development environment it works prefect.