Mongoid unable to create 1-N referenced docs in embedded documents

1_N_embedded_error.rb

class Email
  include Mongoid::Document
  field :emailid, type: String
  embeds_many :account
end

class Account
  include Mongoid::Document
  field :number, type: Integer
  field :openedon, type: DateTime
  embedded_in :email #Email has one field of type String. Not defined here.
  has_many :shadows
end


class Shadow
  include Mongoid::Document
  field :shadowdate, type: DateTime
  field :balance, type: String
  belongs_to :account
end


# This fails with the error:
# NoMethodError: Undefined method 'keys' for DateTime:Class

# Replacing has_many :shadows to embeds_many :shadows seems to do the trick. Mongoid 
# not able to reference documents in embedded documents.