To illustrate the issue, I started from the [Qt]/Examples/Qt-5.3/widgets/mainwindows/mainwindow example. I modified it in such a way that a new dock widget consists of a QWebView rather than a QTextEdit. I also load the www.qt-project.org URL (it would seem that everything is fine if no URL is loaded). See the modified code is attached.

If you build the example, run it, add a dock widget, move that dock widget from one dock site to another, then eventually the example will crash. Attached is the crash report that I for example got on OS X 10.9.4.

FWIW, I have a copy of my application that was built against Qt 5.2.1 and everything is fine.