I noticed that deleted users still show in the count of the users admin screen.
On one blog I deleted 9 users only leaving the admin but it stil shows 9 in the count. In the physical database they are no longer present in the wp_users and wp_users_metadata so.... i guess that the counter is uhm... somewhere else in the database and I set it tot 1 manually in the database??
update / fix
I notice that the records wp_capabilities and wp_user_level do not get deleted in the wp_usermeta table after deletion
after I deleted those 2 records manually in the database the count was back to 1