node.js + socket.io + redisstoreで何故かソケット情報が蓄積する。

repro.js

var SERVER_PORT = 80;
var LIFE_TIME = 30000;
var REDIS_HOST = "xxx.xxx.xxx";
var REDIS_PORT = 6379;

var http = require('http');
var io = require('socket.io');

var server = http.createServer();
var manager = null;
var namespace = null;
var diff = 0;

function initSocket(socket) {
    setTimeout(function() {
        socket.disconnect();
    }, LIFE_TIME);
    socket.join("test.1234");
    socket.on("disconnect", function() {
        diff -= 1;
    });
}

function countup(dict) {
    var res = 0;
    for(var i in dict) {
        res += 1;
    }
    return res;
}

server.on("request", function(req, res) {
    if (namespace) {
    	// 管理情報を表示
        var log_params = {
            count : countup(namespace.sockets),
            trans : countup(manager.transports),
            hands : countup(manager.handshaken),
            connects : countup(manager.connected),
            opens : countup(manager.open),
            closes : countup(manager.closed),
            rooms : countup(manager.rooms),
            roomClients : countup(manager.roomClients)
        }

        console.log("clients", log_params);
    }
    res.writeHead(200, {'Content-Type': 'text/plain'});
    res.end("end");
});

var configure = {
    'polling duration': 2,
    'close timeout': 20
};
manager = io.listen(server, configure);

// RedisStoreを利用するとソケット情報が蓄積する
var options = {
    redisPub: {port: REDIS_PORT, host: REDIS_HOST},
    redisSub: {port: REDIS_PORT, host: REDIS_HOST},
    redisClient: {port: REDIS_PORT, host: REDIS_HOST}
};
manager.set("store", new (require('socket.io/lib/stores/redis'))(options));
namespace = manager.sockets.on("connection", function(socket) {
    diff += 1;
    initSocket(socket);
});

server.listen(SERVER_PORT);