Terminal Session - Restric each user to one session is unstable to some user

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http://serverfault.com – I have enable - Restrict each user to one session in Window Server 2003 R2 Standard edition, which is my terminal Server.Please see the below screen, but sometime some user are able to take two session i.e in task manager it shows one disconnected and one active. Can you tell me, why it showing like that? Note:- After making the changes in Terminal Services Configuration, i had restarted the server earlier. (HowTos)