IE 9 failed to fire DISPID_ONQUIT event?

[forester]

The following code is for a toolbar to revceive DWebBrowserEvents2 events from Internet Explorer. Running on IE 8 and 7, the toolbar can catch both DISPID_DOCUMENTCOMPLETE and DISPID_ONQUIT events. On IE 9, the tooblar receives only DISPID_DOCUMENTCOMPLETE, the message box "Document load complete" will show when I open IE. But the toolbar can not receive DISPID_ONQUIT, the message box for "IE CLOSE event" never appears when I close IE 9, it looks like that IE 9 does not fire DISPID_ONQUIT event. Does IE 9 forget to fire this event? Thanks for any help!

STDMETHODIMP CMyIEToolBar::Invoke(DISPID dispidMember, REFIID riid, LCID lcid, WORD wFlags,   
                                DISPPARAMS* pDispParams, VARIANT* pvarResult,   
                                EXCEPINFO*  pExcepInfo,  UINT* puArgErr) 
{
		HRESULT		lResult = S_OK;

		if (!pDispParams)
			return E_INVALIDARG;

		switch (dispidMember)
		{

		case DISPID_DOCUMENTCOMPLETE:   
                  MessageBox(NULL, _T("Document load complete"), _T("DOCUMENT COMPLETE"),MB_OK);   
                  break;   

		case DISPID_ONQUIT:
		//case DISPID_QUIT:
		  MessageBox(NULL, _T("IE  CLOSE event"), _T("IE close"),MB_OK); 
		  ManageConnection(Unadvise);
		  break;   

		default:
		  break;

		}
		return lResult;
}