Class implementation not recognized

I have the following code:


Class A extends MovieClip implements IClass
{

}

Class A is the entry point class for a particular section of my application. Class B is a parent class that loads the resulting compiled Class A swf. In Class B I check for the following:


onLoadSwfComplete(e:Event):void
{
var displayObject:DisplayObject = _loader.contentLoaderInfo.content;
trace('is IClass: ' + Boolean(displayObject is IClass));
}

The above trace statement evaluates to FALSE. Any ideas as to why? I had this working originally when I was compiling via the Flash IDE. It broke as soon as I started compiling with the flex compiler (ver. 2.0.1).