Fixtures with serialized attributes are not properly loaded

Having a model with serialized attributes (as an Array or Hash) doesn't allow to create YAML fixtures for them. Example:

class User
  serialize :preferences, Hash
end

And a corresponding fixture:

User1:
  id: 1
  preferences:
    sort: 'name'
    lines: 50

When loading that fixture (which does not instantiate ActiveRecord model), such values are simply be inserted as Hash#to_s instead of Hash#to_yaml, causing the ActiveRecord class to complain when instantiating those records from the database (Expected Hash, got String).

This is a change in behaviour from Rails 2.3, which converts such values to YAML. The change was introduced in ActiveRecord::ConnectionAdapters::Quoting (file active_record/connection_adapters/abstract/quoting.rb) where the quote method simply calls value.to_s, whereas the same method in Rails 2.3 would call value.to_yaml.

Is there a reason why Objects are no longer serialized as yaml, but simply converted to String when quoted for SQL insertion?