MongoDB association oddity with Factory Girl

so i had the following associations...

Product
  embeds_many :pressings
Pressing
  embedded_in :product
  embeds_many :variations
Variation
  embedded_in :pressing

after realizing referencing associations would better suit my needs, the associations became...

Product
  references_many :pressings
Pressing
  referenced_in :product
  references_many :variations
Variation
  referenced_in :pressing

and now when i run my Factory Girl factories...

Factory.define :product do |product|
  product.after_create    { |p| 5.times { Factory(:pressing, :product => p) } }
end
Factory.define :pressing do |pressing|
  pressing.after_create   { |p| 5.times { Factory(:variation, :pressing => p) } }
end
Factory.define :variation do |variation|
end

the products and pressings are associated together properly, but the pressings and variations are not, even though the variations are being created. the oddity can be seen in the following commands...

>> v = ProductVariation.first
=> #<ProductVariation _id: 4d9acc89e1607c48fd00001c, _id: BSON::ObjectId('4d9acc89e1607c48fd00001c'), _type: nil, pressing_id: BSON::ObjectId('4d9acc89e1607c48fd00001b')>
>> v.pressing.product.pressings.first.variations
=> []

you can see that i start with an existing pressing... work my way up to the product, and then back down to view all variations... but the count is 0. how can this be?