with my activex control, IE process not quit after close window/pages

[youcl]

I am building an activex dll with Qt. I subclass QAxFactory to create the exported class object and use singleton pattern.

//MyFactory is subclass of QAxFactory
//MyClass is the exported class for com container to use
QObject *MyFactory::createObject(const QString &key)
{
    return MyClass::getInstance();
}

Here is the problem:

After refresh the IE page several times, then close the IE page/window, the exported class MyClass's deconstruction gets called immediately, but MyFactory's deconstruction not. And in windows task manager, the iexplorer process does not quit. After about 30~50 seconds, the iexplorer process quit and MyFactory's deconstruction gets called.

I guess this is because my code did not clear some resources correctly, but I could not found what resource.

Is there a way I can debug this problem? Thanks in advance!

update
It looks like event handler did not get released properly in js. Following is the event handler functions in js.

function MyClassObj::eventHandler()
{
    console.log("event fired");
}

How do I release the handler properly when page get refreshed or closed?