When updating the "scope" attribute, the element is not "added" to the current list

[RiceT-zz]

Hi all
Models (Rails 3 application):
class NetworkService < ActiveRecord::Base
has_many :network_classes, :foreign_key => "network_id", :order => :position
end
class NetworkClass < ActiveRecord::Base
belongs_to :class_definition, :foreign_key => "class_id"
belongs_to :network_service, :foreign_key => "network_id"
acts_as_list :scope => :network_id
validates_presence_of :class_id, :network_id
attr_accessible :class_id, :network_id
end

Case:

• when I create an element in NetworkClass, no problem it goes straight at the end of the current list.
• when I update the "network_id" attribute which holds the "scope", the record is saved with a "position" set to 1, no matter if there are already records with the same "network_id". I would expect that the "position" of the updated record is set to the (last position + 1) of the list corresponding to the new "network_id" value. You then end up with multiple records with the same position in the list.
• note: the NetworkClass "belongs to" another "class_definition" table, but not concerned with the list (I guess)

Many thanks for the gem anyway