When saving an mhtml page QWebEngineDownloadRequest::isSavePageDownload() returns false

When saving a webpage to MHTML, the associated QWebEngineDownloadRequest returns the following values:

• isSavePageDownload() => true
• mimeType() => "application/x-mimearchive"

However, when the current webpage is already an MHTML file, saving the page gives a QWebEngineDownloadRequest with the following values: 

• isSavePageDownload() => false
• mimeType() => "multipart/related"

Step 1

The initial MHTML file is created from a web page by using 

QWebEnginePage::triggerAction(QWebEnginePage::SavePage); 
//or
QWebEngineView::triggerAction(QWebEnginePage::SavePage); 

The download request is handled with QWebEngineProfile::downloadRequested().

Step 2

The MHTML file is then opened with

auto page = new QWebEnginePage();
page->setUrl(QUrl::fromLocalFile(pathToMhtml);

Step 3

Finaly a new SavePage action is triggered just like in step 1.