url_for doesn't work correctly for nested resources

If I create 2 scaffolds, for example Shop and Product and create nested routes so that

resources :shop do
  resources :product
end

Then, in the view, shop_products_url(@shop, @product) produces /shops/1/products/1 correctly,
but in the controller, shop_products_url(@shop, @product) produces /shops/1/products.1
(also _path is affected).

As for testing:

post :create, :product => @product.attributes, :shop_id => @shop.id
assert_redirected_to shop_products_path(@shop, assigns(:product))       # Success
assert_redirected_to "shops/#{@shop.id}/products/#{@product.id}"        # Fail <shops/1/products.1>

I'm able to reproduce this with 1.8.7, 1.9.1, 1.9.2-head and rails3 beta3 and rails3 edge.