Changes in user reflects on admin?
 

I've got a test user and an admin.

I changed the email address in the user cp of the test user into a non-existent email address.

The usergroup options then changed to 'Users awaiting Email confirmation'.
When I logged in with this test user's name and password, I couldn't access the main page. I just couldn't log in.
When I logged in with my own account, this test user wasn't visible on the Member's List.

I then changed the usergroup options, the primary usergroup to 'registered users' and I changed the 'additional usergroups' to 'confirmed users' which is a new group I made since all users have to be confirmed by an admin to be able to visit all of the boards.

Then the admin couldn't post anymore in one board; a board that is only visible to admins.

When I reversed the changes I made to this test user (the primary usergroup to 'users awaiting email confirmation' and 'additional usergroups' to 'none' and the one in between (forgotten that name) to 'standard' the admin could post again in that certain board.

Now how can it be that changes made to one user reflects on an admin?

The funny thing also was that the email we have for the forum itself received the email that this test user should've gotten (if the email I changed it to did exist). Now why would the system sent an email to the forum email if it was supposed to sent this email to the given (changed) email from this test user?