you need to assign the fontfamily to a style class in your css file:
and in your button skin class apply the style class to the label:
<s:Label id="labelDisplay" styleName="customBtnFontStyles"
and you should see something like this:
In the last version, I didn't use a swf.
Could you please give me your Fxp ?
Which version of sdk did you use ? 4.6 ?
That is strange. I'm using Flashbuilder Premium 4.6 for mac.