Forms on partial doesn't render properly

I have a Rails app that is running fine on Rails 3.x and ActiveAdmin 0.6.6. However I want to upgrade it to Rails 5 and ActiveAdmin 1.x. I started the upgrade process first upgrading from 3.x to 4.x and then to 5x, and with ActiveAdmin I tested with 1.0.0 and now I'm using the master from Github.

Everything worked fine with the App in both Rails versions and ActiveAdmin but the ActiveAdmin forms that are in a partial.

The problem is the following:

I have a file app/admin/menu.rb whose has a partial views/admin/menus/_form.html.erb. The partial contains the form of the Menu.

This is the contents of the partial (views/admin/menus/_form.html.erb):

<%= semantic_form_for [:admin, @menu], builder: ActiveAdmin::FormBuilder do |f| %>
  <% f.inputs 'Campos Menu' do %>
    <% f.input :project if current_admin_user.admin? %>
    <% f.input :title %>
    <% f.input :title_en %>
    <% f.input :item %>
    <% f.input :icon, as: :file %>
  <% end %>
  <% f.inputs 'Submenus' do %>
    <% f.has_many :submenus, heading: '' do |fa| %>
      <% fa.input :title, as: :string %>
      <% fa.input :title_en, as: :string %>
      <% fa.input :kind, as: :select, collection: Submenu.kind_collection %>
      <% fa.input :items_as, as: :select, collection: Submenu.items_as_collection %>
    <% end %>
  <% end %>
  <% f.actions do %>
    <% f.action :submit %>
  <% end %>
<% end %>

The render result of this file is only the 'actions' buttons, in this case the 'submit' button. The interesting thing is that if I remove the <% f.actions do %>... from the partial then the <% f.inputs 'Submenus' do %> gets rendered and the same if I remove the later. In other others is being rendered on the last block that contains an end.

The same behaviour is being observed on Rails 4.x and 5.x (except Rails 5.1.x which I didn't tested).

If I move the form from the partial to the app/admin/menu.rb it gets rendered properly. This could be a solution for me however I have others forms that make use of JQuery for fields manipulation and other stuff on the front end.

As I said before, all these forms partials were working properly on Rails 3.x and ActiveAdmin 0.6.6.

Anyone knows what's the problem?

DISCLAIMER: I'm not a Rails or ActiveAdmin expert, so bear with me if is a silly mistake related to this issue.