When a TFTP request response arrives that incorrectly specifies its source port as the control port, the request should be rejected with an error code 5 (TFTPErrorPacket.UNKNOWN_TID) and suggested text "INCORRECT SOURCE PORT".
This can happen when an incorrectly written TFTP server replies to a request from a control socket instead of building a new socket that attaches to an ephemeral port.
Note 1: The expected response from a read request is a DATA packet. The expected response from a write request is an ACK packet.
Note 2: The control port is implementation specific and not always port 69 (as defined by IANA).