ActionScript 2.0 :: Unloading An External Swf Using The MovieClipLoader Object?

I"m having a tiny problem with unloading an external swf using the MovieClipLoader object. This is what I"m doing:

Code:
if (mcLoader.unloadClip(container)) {
trace(container.testVar) // shows testVar
}
button.clickHandler = function () {
trace(container.testVar) // says undefined when clicked
}

So what's happening is right after I call unloadClip it's still loaded however if I click the button at some point after unloadClip is called it shows that is has been unloaded. So obviously there's a little bit of a delay while things are being unloaded. My question is, does anyone know of a way to detect when the clip is unloaded like with an event listener or something? I want to be able to load up another swf after one is unloaded for the level maps for my game I'm working on.