User information not getting if it is a same user

A checklist has many task_status, I have displayed the view in nested model atttributes form, checklist_instance attributes and its associated nested attributes are getting updated correctly. while i try to update user information to the checklist instance, the following updates only if the updated_by_user is not same as @authenticated_user.

def update @checklist_instance.attributes = params[:checklist_instance] @checklist_instance.updated_by_user = @authenticated_user if         flash[:notice] = 'Checklist was successfully updated.'         redirect_to_edit end end

Could anyone suggest me a solution for this..