[OS X] Web Engine renders initially at 1/2 size on Retina Displays

QWebEngineView renders its contents at half size when initially shown. If the content is refreshed (right click->Refresh), then HTML content renders at the full size of the widget.

Note the issue is only reproducible on OS X Retina displays.

The fancybrowser example can be used to reproduce the issue. Only replace the:

   url = QUrl("http://www.google.com/ncr");

with the Test.html file attached here.

What's also interesting is that the web engine view/page knows its correct size. For example, if you move the cursor around on the page that tracks mouse position, the correct position is reported by the javascript. If you create a html sprite to follow the cursor, the sprite appears in the 1/2 size rendered corner but correctly shows the mouse position in the full size view.

This suggests that it is purely a rendering issue. The functionality of the
page, including mouse position and events, is correct even though it is
rendered incorrectly (until reloaded).