PDU Size is 0 if no connection can be established

Original report by Martin Nöhrer:

I've found a bug that prohibits re-connections if the connection to the PLC is lost. The PDU size will be set to 0 if no PLC is available. In a later connection request the PDU size of 0 will be requested during the communication setup. The PLC will close the TCP connection with an error 66 and no connection can't be established anymore.