I found the reference in the standard HL7 specification Chapter 2 (2.12.1.2.1) relating to acknowledgement messages:
“The MSH segment in the response is constructed anew following the rules used to create the initial message described above. In particular, MSH-7-date/time of message and MSH-10-message control ID refer to the response message; they are not echoes of the fields in the initial message. MSH-5-receiving application, MSH-6-receiving facility, and MSH-11-processing ID contain codes that are copied from MSH-3-sending applica
