Creates invalid users when importing work items

Problem1: when importing work items invalid users are beginning created

Problem 2: or it defaults the user name that has been archived instead of defaulting the valid user

Assumption:  We know the user name has to match exactly to user name stored in user database

Question 1: Why does the import create users that are not in the user database?

Question 2: Why does it default an  archived user name instead of the valid user name

If I import a large amount of work items and the users are invalid or its using an archived user name then the user does not receive email regarding the action item assigned to him.

The import itself is a matter of minutes but to have to review each workitem for every user field on the form to verify the correct user has been defaulted takes hours, (time I don't have)

I need a solution when importing not to create invalid users and using the archived user name instead of a solution

or is there not a solution?