WebEngine becomes black when calling winId() on another widget

Using Qt 5.5.1, WebEngine from today's Git and 47-based Chromium. When I call winId() on some widget, WebEngine becomes black. Quick and dirty sample project is attached. Steps to reproduce:

1) compile and run:

$ qmake && make
$ ./webeng3 file://$PWD/w.html

2) Enter some URL in the appeared window

Result:

The application will load the specified URL into the WebEngine widget, then call winId() on the plugin. After calling winId(), WebEngine becomes completely black.