I checked out a user profile and see what is happening.

Before the import, the URL in a user profile is:
http://www.mydomain.com/ubb/Avatars/avatarfile.gif

After the import, the URL becomes:
http://www.mydomain.com/home/ubb/Avatars/avatarfile.gif

The insertion of "home" is the problem.

Anything I can do to prevent that before I run the importer again?