has_many_through_associations and delete with dependent

Hi

let's say I've the following associations

class User < ActiveRecord::Base
    has_many :user_network_privacies, :dependent => :destroy
    has_many :networks, :through => :user_network_privacies
end

class UserNetworkPrivacy < ActiveRecord::Base
   belongs_to :user
   belongs_to :network

   before_destroy { puts "my before_destroy callback" }
end

I would expect the before_destroy to be called when I do
a_user.networks.delete(a_network) wich is true in rails 1.2.3 (my
actual version) but not in rails 1.2.6 (my target version).
If anybody has some explanations, the only thing related I see in
active record changelog is on version 1.15.6
* Fix has_many :through delete with custom foreign keys. #6466
[naffis]

Thanks in advance
Niko