Post directive in nested singleton resource route doesn't work

On POST in the browser:

Routing Error

No route matches "/account/passphrase/authenticate"

But it does too, dammit!!!

In fact, I know this because GET /account/passphrase/confirm_destroy works fine!!!
It's only the post directive under a nested singleton resource that doesn't work.

In routes.rb:

resource :account, :controller => :account, :only => [:show, :edit, :update] do
  # this is NOT the actual account password, it's something else!!!!
  resource :passphrase, :controller => 'account/passphrase' do
    post :authenticate
    get :confirm_destroy
  end
end

rake routes are correct:

authenticate_account_passphrase POST /account/passphrase/authenticate(.:format) {:action=>"authenticate", :controller=>"account/passphrase"} confirm_destroy_account_passphrase GET /account/passphrase/confirm_destroy(.:format) {:action=>"confirm_destroy", :controller=>"account/passphrase"}

            account_passphrase POST   /account/passphrase(.:format)                 {:action=>"create", :controller=>"account/passphrase"}
        new_account_passphrase GET    /account/passphrase/new(.:format)             {:action=>"new", :controller=>"account/passphrase"}
       edit_account_passphrase GET    /account/passphrase/edit(.:format)            {:action=>"edit", :controller=>"account/passphrase"}
            account_passphrase GET    /account/passphrase(.:format)                 {:action=>"show", :controller=>"account/passphrase"}
            account_passphrase PUT    /account/passphrase(.:format)                 {:action=>"update", :controller=>"account/passphrase"}
            account_passphrase DELETE /account/passphrase(.:format)                 {:action=>"destroy", :controller=>"account/passphrase"}

In the controller:

class Account::PassphraseController < ApplicationController
... # GET /account/passphrase # form for authenticating def show

@keypair = current_account.keypair

end

# POST /account/passphrase def create

...

end

# POST /account/passphrase/authenticate def authenticate

@keypair = current_account.keypair
...

end end

In the view:

Please enter your secret passphrase.

<%= form_for @keypair, :url => authenticate_account_passphrase_path do |f| %> Route works fine in the view: authenticate\_account\_passphrase\_path And in rake routes. What's with the??? Routing Error No route matches "/account/passphrase/authenticate" When GET /account/passphrase/confirm_destroy works fine???