Unlimited field - when clicked on the add another item the relation select field desapears.

On a fresh Drupal install, with only the requiered modules to make relation select works (views, ctools, subform, efq, relation):

1. Create a dummy relation, leave all default with all node bundles as source
2. Add a relation select field to the basic page content type, with number of values set to unlimited
3. Generate some content
4. edit a basic page, on the relation select form, click on add another item.

The result: the whole relation select field/form disappears.

Looking at the html, when the add another item is clicked, only

<div id="edit-field-test" class="field-type-relation-select field-name-field-test field-widget-relation-select form-wrapper">
  <div class="ajax-new-content" style="display: block;"></div>
</div>

is left, no error message in the firebug console.

I tried to debug it with no luck so far.

Is anyone having the same problem?