ActiveRecord: validates_associated not working when updating a model?

I have 2 models:

class Book < ActiveRecord::Base
  has_many :book_versions
  accepts_nested_attributes_for :book_versions, allow_destroy: true
  validates_associated :book_versions

class BookVersion < ActiveRecord::Base
  has_many :collection_items
  has_many :collections, through: :collection_items
  belongs_to :book
  validates_presence_of :price, :isbn #<-- validates presence

Everything works fine and dandy when I go to books / new and create a book with several book versions. Validations work when I leave the price or isbn empty.

However, after creating a book with several book versions, I return to the editing form and I delete one of the prices of the existing linked version_book, and I submit the book form, it "successfully updates the book." There are two problems here:

• validates_presence_of :price does not start
• The version is not really being updated.

Here is a copy of part of the parameters:

"book_versions_attributes" = > { "0" = > { "name" = > "alt", "isbn" = > "," price" = > "," famis_number" = > "," famis_price" = > "," weight_in_pounds "= > " "}," 1" = > { "name" = > "bb", "isbn" = > "123123123123222222 "," price" = > "," famis_number" = > "," famis_price" = > "," weight_in_pounds "= > " 1.0 "," inventory "= > " 08 "," id "= > " 1030"},...

"", , bb book_version - .

?