Adding ui.tooltip

Hi there --

I installed the 7.x-2.x-dev version and then:

drupal_add_library('system', 'ui', true);
drupal_add_library('system', 'ui.tooltip', true);

and I see:

/sites/all/modules/jquery_update/replace/ui/ui/minified/jquery.ui.core.min.js

being added, but not the tooltip code. I alternatively tried:

drupal_add_library('jquery_update', 'ui.tooltip', true);

in desperation, since ui.tooltip was introduced in jQuery ui 1.9, but to no avail.

Any idea what I'm missing?

Thanks in advance,
Carlos