Consider this simple piece of code:

void func()
{
    QProcess().execute("ls");
}

int main(int argc, char *argv[])
{
    QCoreApplication app(argc, argv);
    QtConcurrent::run(func).waitForFinished();
}

With Qt 5 (last qtbase commit: 83b1ed1ea8168e3de15de7a8a44a5224db5a2284), this application hangs indefinitely in the execute() call. Calling start() and then waitForStarted() shows the same behavior.
The same code works fine with 4.8. It also works fine if you do not create a QCoreApplication object.