Cannot connect with the MongoDB superuser to the other databases from the terminal

I have defined a superuser in my admin database:

$ mongo admin -u superuser -p 1234
MongoDB shell version: 2.4.6
connecting to: admin
> db.system.users.findOne()
{
    "_id" : ObjectId("52a9a8bd2db854b07d3960f1"),
    "user" : "superuser",
    "pwd" : "8c246ca972a74c8049b79771df9b718b",
    "roles" : [
        "userAdminAnyDatabase",
        "dbAdminAnyDatabase",
        "clusterAdmin",
        "readWriteAnyDatabase"
    ]
}

But now I cannot connect to another database with this user:

$ mongo mono -u superuser -p 1234
MongoDB shell version: 2.4.6
connecting to: mono
Thu Dec 12 13:22:42.100 Error: 18 { code: 18, ok: 0.0, errmsg: "auth fails" } at src/mongo/shell/db.js:228
exception: login failed

Is this a know feature/limitation or am I doing something wrong?