Active Admin scopes for each instance of a related model

I have an issue with a dynamic active admin scope. I am attempting to create a scope for each "manager" of a "project" in my app. However, the scopes don't seem to update when a new manager is created (or assigned to a project) but they DO update if I restart the server. So the code "works" per se but obviously not in the way I would like it to. I'm a ruby/rails noob so I am not sure if I need to do something to "refresh" the scope in some way.

As an FYI, I am using Rails 3.2 on Heroku Cedar with ActiveAdmin

Here is the code in question (that works but only brings in new managers after the server is restarted):

Manager.find_each do |m|
  scope m.first_name do |projects|
    projects.where(:manager_id => m.id)
  end
end

And the entire Active Admin Project model:

ActiveAdmin.register Project do
 menu :priority => 1
 index do
  column :name
  column :company_name
  column :status
  column :projection do |project|
   number_to_currency project.projection
  end
  column :updated_at
  default_actions
 end

 scope :all
 scope :working, :default => true do |projects|
  projects.where(:status => 'working')
 end

 Manager.find_each do |m|
  scope m.first_name do |projects|
    projects.where(:manager_id => m.id)
  end
 end
end