if $('my_tooltips_selector').tooltip() is called more than once, during the subsequent calls to tooltip(), the code assumes that all of the instances still exist if any of the tooltip instances still
exist -- even if some of them no longer exist.

specifically, api will be true (https://github.com/jquerytools/jquerytools/blob/master/src/tooltip/tooltip.js#L322) if there are any existing tooltips, even if many items returned by this.data("tooltip") are null. so, if any parts of a page with tooltips are refreshed via ajax, new tooltips will not appear on the refreshed items even if they are still properly selected and called a second time by $('my_tooltips_selector').tooltip()

instead, each item in this.data("tooltip") should be examined so tooltip can be recreated if the item is null, and existing tooltips can be ignored