Rails Active Admin: Why isn't my custom form rendering any inputs?

Question

Rails 3.1.1
Active Admin 0.4.4
formtastic 2.1.1

This is the active admin controller for my Agency model.

ActiveAdmin.register Agency do
  form do |f|
    f.input :name
    f.input :contact_email, :label=>"Email invoices to"
    f.input :api_key, :hint=>"Create a key by following <a href=\"#\" target=\"_blank\">these instructions</a>".html_safe
    f.actions
  end
end

The form should render the three inputs, followed by the submit button, but all I get is:

Just to be clear, the HTML shows no signs of the missing inputs:

<form accept-charset="UTF-8" action="/admin/agencies" class="formtastic agency" id="agency_new" method="post" novalidate="novalidate" name="agency_new">
  <div style="margin:0;padding:0;display:inline">
    <input name="utf8" type="hidden" value="✓"><input name="authenticity_token" type="hidden" value="...">
  </div>
  <fieldset class="actions">
    <ol>
      <li class="action input_action" id="agency_submit_action">
        <input name="commit" type="submit" value="Create Agency">
      </li>
    </ol>
  </fieldset>
</form>

I also tried using fieldsets, with the same (faulty) output:

ActiveAdmin.register Agency do
  form do |f|
    f.inputs "New Agency" do 
      f.input :name
      f.input :contact_email, :label=>"Email invoices to"
      f.input :api_key, :hint=>"Create a key by following <a href=\"#\" target=\"_blank\">these instructions</a>".html_safe
    end
    f.actions
  end
end

Update: I've discovered that commenting out the f.actions line gets formtastic to actually print the inputs, but now just without the button.

ActiveAdmin.register Agency do
  form do |f|
    f.inputs "New Agecny" do 
      f.input :name
      f.input :contact_email, :label=>"Email invoices to"
      f.input :api_key, :hint=>"Create a key by following <a href=\"#\" target=\"_blank\">these instructions</a>".html_safe
    end

    #f.actions
  end
end

Form with inputs but no button:

Answer 1

Try using this: f.buttons :submit

I also think that the block for buttons/actions changed a bit in a version of active admin at some point, so you may be tripped up by old tutorials, etc.