Different ConnectionId for Connect/OnDisconnected method in same browser window SignalR

Question

I am working on chat client for my web app and i am stuck on interesting problem with different ConnectionIds which i receive from Hub Context, when i log in my app i get ConnectionId from Hub context and i store it into my list, when i close tab in browser my OnDisconnected method is reached but with different connectionId even when all events happened in same browser tab.

        static List<ApplicationUser> onlineUsers = new List<ApplicationUser>();

    #region Connect
    public void Connect(string userName)
    {
        var id = Context.ConnectionId;

        var userDetails = new ApplicationUser
        {
            ConnectionId = id,
            UserName = userName,
        };

        if (onlineUsers.Count(x => x.ConnectionId == id) == 0)
        {
            onlineUsers.Add(new ApplicationUser { ConnectionId = Context.ConnectionId, UserName = userName });
            Clients.Others.newOnlineUser(userDetails);
            Clients.Caller.getOnlineUsers(onlineUsers);

        }
    }
    #endregion

    #region Disconnect
    public override Task OnDisconnected(bool stopCalled)
    {
        var item = onlineUsers.FirstOrDefault(x => x.ConnectionId == Context.ConnectionId);
        if (item != null)
        {
            onlineUsers.Remove(item);
            Clients.Others.newOfflineUser(item);
        }
        return base.OnDisconnected(true);
    }

Any idea what may cause this problem?