routing: namespace ignored inside resources

Using Rails 2.3.5, the following route definition:

map.resources :users do |users|

users.namespace :admin do |admin|
  admin.resources :products
end

end

should produce a route:

user_admin_product GET /x/users/:user_id/admin/products/:id

but it actually produces:

    user_product GET    /users/:user_id/products/:id

i.e. the 'admin' namespace gets lost.

Note however if I nest this all inside a top level namespace, the inner 'admin' namespace reappears:

map.namespace :x do |x|
map.resources :users do |users|

users.namespace :admin do |admin|
  admin.resources :products
end

end

x_user_admin_product GET /x/users/:user_id/admin/products/:id