I've found a bug in ui.tooltip: tooltip interrupts closing if its content is changing. Here is example.
Please help me to make proper test, this one fails from time to time on "tooltip was hidden too early":
PHP Code:
asyncTest"content: change while close", function() {
    
expect);
    $.
fx.off true
    
var tooltip,
        
hidingDuration 20,
        
element = $( "#tooltipped1" ).tooltip({
            
hidehidingDuration
        
});

    
element.tooltip"open" );
    
tooltip = $( "#" element.data"ui-tooltip-id" ) );

    $.
fx.off false;
    
element.tooltip"close" );
    
setTimeout( function() {
        
oktooltip.is":visible" ), "tooltip was hidden too early" );
    }, 
hidingDuration 10 );


    
setTimeout( function() {
        
ok( !tooltip.is":visible" ), "tooltip doesn't hid properly" );
        
start();
    }, 
hidingDuration 10 );
});