Rails ActiveRecord associations autosave option

I have the following associations.

class Document < ActiveRecord::Base   has_many :document_sections, :dependent => :destroy, :autosave => true   has_many :document_items, :through => :document_sections end

class DocumentSection < ActiveRecord::Base   belongs_to :document   has_many :document_items, :dependent => :destroy, :autosave => true end

class DocumentItem < ActiveRecord::Base   belongs_to :document_section end

When I use irb console to do

d = Document.find_by_id(100) d.title = '1-comments' s = d.document_sections.find_by_id(200) s.title = '2-comments' i = s.document_items.find_by_id(10) i.comments = '3-comments' d.save

The changes to d, s, and i get saved to the database because of the autosave option set to true in the model. However when I do the same in a controller action, only the document header comments get saved. The log only shows a sql update to the documents table but not the document_sections and document_items table. Why is this behavior different in a controller vs irb console.