QtWebEngine not rendering background transparent when transparency is set AFTER page load

A bit more about the history of this (I am TheSHEEEP there):
http://stackoverflow.com/questions/28183738/transparent-background-in-qwebenginepage/36439487

When you set the background color of a QWebEnginePage to Qt::transparent AFTER the first page has loaded (as a reaction to signal QWebEngineView::loadFinished ), the background of the QWebEngineView will not be transparent, but white.

It seems to me that the background color setting of the page only leads to a transparent background of the QWebEngineView if set before the page is loaded. Otherwise, it will indeed set the background of the page to be transparent, but there will be a white background behind the page (making the transparency kinda worthless).