Why is AS3 underlining certain fonts but not others (all of which are pretty common)?

Question

Hello everyone!
     I have a simple question that hopefully has a simple answer (which mocks me with its elusiveness). In the code below (taken from Gary Rosenzweig's "ActionScript 3.0 Game Programming University" (2nd ed.)), I am declaring a simple style sheet using all AS3 supported tags/attributes to underline an HTML link. My question is this: why won't AS3 underline the chosen font (Arial) but yet it will underline certain other fonts that I substitute it for (such as "Times New Roman" and "Garamond")?
// create a basic format
var myFormat:TextFormat = new TextFormat();
myFormat.font = "Arial";
myFormat.size = 24;
myFormat.bold = true;
var myStyleSheet:StyleSheet = new StyleSheet();
myStyleSheet.setStyle("A",{textDecoration: "underline", color: "#0000FF"});
// create a text field with a Web URL link
var myWebLink:TextField = new TextField();
myWebLink.defaultTextFormat = myFormat;
myWebLink.styleSheet = myStyleSheet;
myWebLink.selectable = false;
myWebLink.htmlText = "Visit <A HREF='http://flashgameu.com'>FlashGameU.com</A>!";
myWebLink.x = 80;
myWebLink.y = 90;
myWebLink.width = 400;
myWebLink.height = 30;
addChild(myWebLink);
var myLink:TextField = new TextField();
myLink.defaultTextFormat = myFormat;
myLink.styleSheet = myStyleSheet;
myLink.selectable = false;
myLink.htmlText = "Click <A HREF='event:testing'>here</A>";
myLink.x = 80;
myLink.y = 190;
myLink.width = 400;
myLink.height = 30;
addChild(myLink);
addEventListener(TextEvent.LINK, textLinkClick);
function textLinkClick(event:TextEvent) {
trace(event.text);

Answer 1

Mr. Murphy,
     You see what I mean? I knew it would be a simple answer - it had to be, right? That way when someone helped me figure it out, I would get the pleasure of kicking myself for not having seen it before. I tried temporarily disabling the default text (thinking maybe it was somehow interfering with the style sheet), ensuring that I had the fonts that I was trying to use embedded in my program, including all the formatting in the actual style sheet rather than some of it resting in the default text statement, and did a couple other things that now escape my memory. What I didn't do was change the font size to see if it was simply cutting off the underscore. Sure I thought about it, but didn't actually follow it up.
     What makes this worse is that, in the book I referenced, the author doesn't say anything about having to change the font size for this particular application and goes further by demonstrating via inline image his "perfect" outputted result using the exact code that I did. I know this threw off other readers as well who tried to emulate his result only to find that the underline magically "disappeared" when they did it.
     Thanks for the help! As always, I appreciate it.