Data posted in the UFD not from mapping

Symptoms:

This is not so much an issue, just a curiosity. I have data showing up in my data base files from elements that are not mapped. How does that happen?

Prescription:

There are two places where values gets posted to the user file without mapping instructions:

1. For the receiving header record format, SET ID Fields can be defined to post the following Partner ID, Mailbox ID and Address ID.

2. For any field in a receiving UFD, a constant can be defined.

Note: For the send UFD however, only the header record format can have a constant or a <keyword> posted can be posted on a field.

BUT if you still do not see it in both cases, hence it should be the default value configured when the file was created.