Topic: How to maintain order of child records when saving nested model?

I am using Rails' nifty accepts_nested_attributes_for feature for creating invoices and their respective items. Items can be added dynamically to an invoice with jQuery.

class Invoice < ActiveRecord::Base
  attr_accessible :project_id, :number, :date, :recipient, :items_attributes
  accepts_nested_attributes_for :items
end

This works fine. Except for the order in which Rails saves the items.

For example when I create an invoice with these 5 items...

    A
    B
    C
    D
    E

... everything works fine. But when I then hit Create to save the invoice plus items to the database, the order is completely randomised, for example like this:

    D
    A
    C
    E
    B

A peek into my database and the created_at column of my items table revealed that Rails (or SQLite?) seemingly saves the items in a random order and not in the order in which I (as a user) added them to the invoice.

Is this normal behaviour and if so how can I maintain a proper ordering on the items that I add to my invoice?

Thanks for any help...