Well,
I think the "ban" type should be based on the available input information.
If someone is trying to logon to a userid -
A) with incorrect password and the "ip address" do not match, the ban should be on the "ip address".
B) with incorrect password and the "ip address" match, the ban should be on the "userid".
C) with correct password and the "ip address" do not match, the ban should be on the "userid".
With this logic, someone else can not trig an admin nickban. The user ban is only trigged if the correct userid/password or the correct user/ip is used.
But, this is just details. This important issue is the automatic ban...