QNativeSocketEnginePrivate::nativePendingDatagramSize implementation for Symbian doesn't handle error which can be in calling ioctl function in correct way.
Upon successful completion, ioctl() shall return a value other than -1 that depends upon the STREAMS device control function.
In this case the function returns another value that -1.

But QNativeSocketEngine::pendingDatagramSize() uses return value to check if socket is valid.
For Symbian it will not work.
I suppose that code should be like

    ssize_t recvResult = -1;
    if ( ::ioctl(socketDescriptor, E32IONREAD, (char *) &recvResult) >= 0 )
        return qint64(recvResult-28);
    return qint64(recvResult);