When you use AL04 and look at each server, your user ID will be shown on each server even though you have not actually logged on to all of the servers. For example, if you logged on to the landscape from "server1", you will see your ID for server1 as well as all the other servers in AL04.
You will see this since you are SAP creates a session for you to get a listing of the number of users logged on to all servers.
A technicality, but you may wonder why your ID is listed on all servers when you have not physically logged in to all servers. The listing of your ID on the other servers is only for the time that you are using AL04. Remember this if you are counting users logged on at one time.