No results querying mongoid with a boolean clause

Question

I am having classes that implement

module CanBePublished

  def self.included(o)
    o.class_eval do
      field :public, type: Boolean, default: false
      scope :published, -> { where(public: true) }
    end
  end

end  

See what happens in a console session:

[1] pry(main)> Portfolio.published.first
=> nil
[2] pry(main)> Portfolio.first
=> #<Portfolio _id: 5391fbc5c1e3dfcf02000001, index: -1, public: "1", title: "test", _slugs: ["test"], description: "portfolio *description*">
[3] pry(main)> Portfolio.where(public: 1)
=> #<Mongoid::Criteria
  selector: {"public"=>true}
  options:  {}
  class:    Portfolio
  embedded: false>

[4] pry(main)> Portfolio.where(public: true)
=> #<Mongoid::Criteria
  selector: {"public"=>true}
  options:  {}
  class:    Portfolio
  embedded: false>

[5] pry(main)> Portfolio.where(public: "1")
=> #<Mongoid::Criteria
  selector: {"public"=>true}
  options:  {}
  class:    Portfolio
  embedded: false>

Just as [1] all these queries return nil. [2] shows that there is an existing object that ought to return from the query.

It seems that the query is always correctly translated with a boolean clause, but in the db the value is persisted as a string and thus does not match the boolean (my impression).

[36] pry(main)> p1 = Portfolio.create({title: 'with params', public: '1'})
=> #<Portfolio _id: 53922082c1e3dfebb9000002, index: -1, public: "1", title: "with params", _slugs: ["with-params"], description: nil>
[38] pry(main)> p1.save
=> true
[39] pry(main)> p1.public == true
=> false

Somehow mongoid or mongo is not translating the "1" to true as it should.

[40] pry(main)> p2 = Portfolio.create({title: 'with params2', public: true})
=> #<Portfolio _id: 5392211ec1e3dfebb9000003, index: -1, public: true, title: "with params2", _slugs: ["with-params2"], description: nil>
[41] pry(main)> p2.save
=> true
[42] pry(main)> p2.public == true
=> true

mongod --version db version v2.6.1

mongoid 4.0.0