Editing an individual with membership "by relationship" alters the "Membership Signup" activity

Recreated on demo site in d6/d7

A membership type has "relationship type" selected, i.e. "employer of", so employees are also added as members, by that relationship.

when an employer is given a membership, the employee is also marked as having that membership and an activity is added to the employee, "Membership Signup"

If the employee contact is now edited and saved, the date and "added by" of that "Membership Signup" activity are altered to match the edit date and the user who edited the contact.

I can't see that this has any other effect, but it is confusing when users see a "Membership Signup" which may actually have occurred long ago.