No tooltip shows up when rolling over a long, abbreviated title on TitleWindow

Steps to reproduce:
1. compile, run following code:

<?xml version="1.0" encoding="utf-8"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009"
xmlns:s="library://ns.adobe.com/flex/spark"
xmlns:mx="library://ns.adobe.com/flex/halo"
width="600" height="600" creationComplete="addPopUp()">
<fx:Script>
<![CDATA[
import mx.core.IFlexDisplayObject;
import mx.managers.PopUpManager;
import spark.components.TitleWindow;
private var tw:TitleWindow = new TitleWindow();
private function addPopUp():void

{ tw = new TitleWindow(); tw.width=300; tw.title="From PopUpManager long long long long long long long long title"; PopUpManager.addPopUp(tw, this, false); }

]]
>
</fx:Script>
</s:Application>

2. mouse over the title string
3.

Actual Results:
no tooltips

Expected Results:

tooltips shows up
Workaround (if any):