I've found a problem, but i don't know if it's a bug of Tooltip or a bug of jQuery itself. What happens it's next:
If i register something like this: $('a').tooltip(), everything goes fine. But, if, i do the same again, the elements registered before, now doesn't have the tooltip anymore, but the news does. I have to do that because i work with templates, so when the page is rendered, with AJAX i process a partial, and the partial has the code for his tooltip's elements. Thanks!!!