Follow the steps to reproduce quirk.
In new installation of WP 2.7
Go to users > authors & users
Most likely there is an "admin" user already. Click Edit for that user.
In the username section it says "Username cannot be changed".
Click on Users > add new.. at the left.
Give some username.
Put in the SAME EMAIL address as that of the admin user.
Put some password and choose user type "Administrator". Click "Add User".
You will be taken to a page that shows only one user (the user you just added) even though at the top it says All (2) | Administrator (2).
That is the quirk. I thought it would show all the users.