QWebChannel does not work with QWebEngine (standalone example)

I tried the standalone webchannel example on Linux (Ubuntu 14.04). It works correctly with the standard browser firefox (Version 43.0). Then I changed the example program to use the Qt WebEngine in the following way:

instead of
QDesktopServices::openUrl(url);

I instantiate a QWebEngineView (I also included QWebEngineView and added webenginewidgets in the list of used modules):

QWebEngineView webView;
webView.load(url);
webView.show();

When I start the new application I have two separate windows. One with the C++ dialog and another with the Web-page.

The C++-Dialog shows the text
Initializing WebChannel...
Initialization complete, opening browser at file:///home/oepnv/work/examples/build-webchannel-Desktop_Qt_5_5_1_GCC_32bit-Debug/standalone/index.html?webChannelBaseUrl=ws://127.0.0.1:12345.

And the Web-Dialog shows:
Connecting to WebSocket server at ws://127.0.0.1:12345.

So the initialization of the WebCannel is not complete and I cannot send messages.

If I open firefox with the printed Url the channel is initialized correctly:

Connecting to WebSocket server at ws://127.0.0.1:12345.
WebSocket connected, setting up QWebChannel.
Connected to WebChannel, ready to send/receive messages!

And I can send messages from there.

I also tried this under WIndows (Windows 7). Here the program crashes the web-view-window.