Embedded document lose reference to parent when parent fails to save

lost_reference.rb

class Account
  include Mongoid::Document

  embeds_many :memberships
  
  field :name, :type => String

  validates_presence_of :name
end

class Membership
  include Mongoid::Document

  embedded_in :account, :inverse_of => :memberships
end

a = Account.new :name => "Awesome"
a.memberships.build
a.save

# No problem;
a = Account.first
a.memberships.first.account # #<Account...>

# Fail;
a = Account.first
a.name = ""
a.save # false
a.memberships.first.account # nil

# Fail;
a = Account.first
a.update_attributes :name => "" # false
a.memberships.first.account # nil