User management / Ghosts

Hello,

After reading the documentation relative to user management, I tried to
modifiy existing users declared in my Domain.xml and there is a strange
behavior that I don't understand :

Context :
I use JAAS to authenticate a user declared in slide (this works nice)
I've renamed the user "root/root" to "admin/admin" in the Domain.xml

Scenario :
I open a connexion using root/root, the connexion succeed !
I open a connexion using admin/admin, the connexion succeed but I got
limited rights

My question is : why does the user root still exists and work ?
Are these informations stored in the associated Store or somewhere else ?

Thanks for your help

     Ektor