default_scope doesn't work on debian

default_scope.rb

# MODEL

class Page
  include Mongoid::Document
  include Mongoid::Timestamps
  include CoverPicture
#....
  field :is_template,           :type => Boolean, :default => false

  default_scope     where(is_template: false )
  scope :templates, where(is_template: true )

# On Mac OS X (Lion preview 3) everything works fine.
# On Debian it doesn't. Page.all is always empty.

# Versions of Ruby, Rails, Mongo, MongoID all the same on both machines.

# Tests
  test "Page select should not include templates" do
    Page.delete_all
    template_page = Page.create(:title => 'This is a template page', :body => "I'm a template", :is_template => true)
    standard_page = Page.create(:title => 'This is a standard page', :body => "Standard")
    sp = Page.first
    tp = Page.templates.first
    assert sp.title == 'This is a standard page', 'First without param is_template should be the standard page'
    assert tp.title == 'This is a template page', 'Using Page.templates.first should be the template page'
  end