YAML, Serialize and Date Formats problem

I'm froma Spain, and was using DATE_FORMATS to allow correct spanish
format of date values. I'm using this at environment.rb file:

ActiveSupport::CoreExtensions::date::Conversions::DATE_FORMATS[:default]
= '%d-%m-%Y'

But using serialize of attributes in ActiveRecord classes give me
problems. I have a simple model like that:

class History < ActiveRecord::Base

serialize :changes

end

Doing this:

History.create({:changes=>{:my_date=>Date.today}})

I can't read changes attribute like an Hash object, it always return a
String object.

Digging deeper,..., I have found that the problem resides on the YAML
library and the format of Date type.

Doing this:

Date.today.to_yaml

=> "--- !timestamp 05-06-2008\n"

But doing this:

YAML.load(Date.today.to_yaml)

ArgumentError: argument out of range

from /usr/lib/ruby/1.8/yaml.rb:133:in `utc'

from /usr/lib/ruby/1.8/yaml.rb:133:in `node_import'

from /usr/lib/ruby/1.8/yaml.rb:133:in `load'

from /usr/lib/ruby/1.8/yaml.rb:133:in `load'

from (irb):1

Reading the YAML Cookbook at http://yaml4r.sourceforge.net/co

I have found that YAML needs Date to be represented by its year, month
and day in ISO8601 order.

¿Why in Rails the YAML/Serialize method don't uses my date format?