Mongoid appends to 'embedded' criteria instead of 'selector' criteria

Mongoid Scoping Issue

class Foo
  include Mongoid::Document
  references_many :bars
end

class Bar
  include Mongoid::Document
  referenced_in :foo
end

f = Foo.create
f.bars << [Bar.create, Bar.create, Bar.create]

b = Bar.scoped :foo_id => f.id
# Note this appends to the 'embedded' attribute instead of the 'selector' attribute
##<Mongoid::Criteria
#  selector: {},
#  options:  {},
#  class:    Bar,
#  embedded: {:foo_id=>BSON::ObjectId('4da31811031af40439000001')}>

b.to_a
# []