How to use QtWebkit and block mixed content?

Question

I am trying to implement a Mixed content blocker (that is, blocks all http:// stuff within https:// page) with QtWebKit.

Here's my primitive implementation so far with subclassed QNetworkAccessManager and reimplemented createRequest()

QNetworkReply *  MyNetworkAccessManager::createRequest ( Operation op, const QNetworkRequest & req, QIODevice * outgoingData)
{
    QNetworkRequest r = req;    /* Take a non-const copy */

    if(this->mainWindow->ui->blockMixedContent_checkBox->isChecked()) { // <-- is Mixed content blocking enabled ?

        QUrl    url(this->URL); // <--- this->URL is the top level URL that is shown on URL bar

        if(url.scheme() == "https") {   // <--- Okay, top level URL scheme is https://
                if(r.url().scheme() == "http") {    // <-- This particular request URL scheme was http:// block it
                    qDebug() << "HALF-ENCRYPTED URL: " << r.url();
                    r.setUrl(QUrl());   // Set url to empty to "block" it 
                }
        }
    }

    return QNetworkAccessManager::createRequest( op, r, outgoingData );
}

Now, when I visit page that test mixed content blocking https://ie.microsoft.com/testdrive/browser/mixedcontent/assets/woodgrove.htm everything is just fine and it blocks both active (scripts) and passive (images) mixed http:// content.

However, when I try to click http:// links from https://startpage.com or when a https:// page redirects me to http:// page or even when I go back in history from https:// page to http:// page it will block me!

So how can I tell not to use mixed content blocking when user clicks http:// link on a https:// page, is being redirected from https:// to http:// site or goes back in history from https:// to http:// page ???

Is there a way, for example, to catch redirects from https:// --> http:// before creatRequest() is called ?

Or could these all checkings be done in createRequest() somehow ???