Missing New_Person Activity

I'm encountering some odd behavior when I upload new people through an email list import.  New persons do NOT have a "New Person" activity logged.  Any ideas on why this is?  Here are more details on my experience:

- Persons were uploaded through a csv List Import

- List import mode was "Default."  I did not select "Skip new people and updates"

- The first activity on the lead's log is "Add to List"

- I have over 700 leads that are affected by this

- I can search for and find these people in the lead database

- These are not duplicates

Any help is very much appreciated! Thank you.