New Post: Callbacks for some host objects are not executing

I obtain the window object in DWebBrowserEvents2_Event.NavigateComplete2 event. Following is some stripped down code snippets:

public void OnNavigateComplete(object pDisp, ref object URL)
{
    var browser = pDisp as IWebBrowser2;
    var document2 = browser?.Document as IHTMLDocument2;
    var window = document2?.parentWindow as IHTMLWindow2;

    var engine = new JScriptEngine("{16d51579-a30b-4c8b-a276-0ff4dc41e755}", null, WindowsScriptEngineFlags.EnableStandardsMode | WindowsScriptEngineFlags.MarshalNullAsDispatch | WindowsScriptEngineFlags.MarshalArraysByValue);
    engine.AddHostObject("window", HostItemFlags.GlobalMembers, window);
}

And the JavaScript snippet:

global is the window object.

contentPort is a private host object.

contentPort.addMessageListener(function (msg) {

    if (global.document.readyState !== "complete") {
        global.addEventListener('load', function () {
            console.log('message document load');
        }, false);
        console.log("Message received - waiting for document load");
    } else {
        setTimeout(function () {
            console.log('message timeout');
        });
        console.log("Message received");
    }
}

The console output displays either "Message received" or "Message received - waiting for document load" but never "message document load" or "message timeout"

The private host object callback works but the window callbacks do not.