Reseeded Identity not showing in GUI
The GUI is showing the result of looking at the table design, which shows IDENTITY(1,1) for the column in question.

Run the following code, then check the definition of the identity value by using the GUI; you will see the GUI reflects the design of the table, which is independent from the actual next value of the IDENTITY column.

USE tempdb;

CREATE TABLE dbo.IdentTest
(
    ID BIGINT NOT NULL IDENTITY(1,1)
);

INSERT INTO dbo.IdentTest DEFAULT VALUES;
SELECT * FROM dbo.IdentTest;

DBCC CHECKIDENT('IdentTest', RESEED, 400000000);

INSERT INTO dbo.IdentTest DEFAULT VALUES;
SELECT * FROM dbo.IdentTest;


After running this, if you look at the GUI, you see:



If you "script" the design of the table; you get the following:

USE [tempdb]
GO

/****** Object:  Table [dbo].[IdentTest]    Script Date: 2015-10-27 4:54:15 PM ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

CREATE TABLE [dbo].[IdentTest](
    [ID] [bigint] IDENTITY(1,1) NOT NULL
) ON [PRIMARY]

GO


Note the scripted table definition still shows IDENTITY(1,1), since that is the definition of the table, which is unchanged by using DBCC CHECKIDENT.  The MSDN page on DBCC CHECKIDENT says the following:


  Checks the current identity value for the specified table in SQL Server 2016 and, if it is needed, changes the identity value. You can also use DBCC CHECKIDENT to manually set a new current identity value for the identity column.


Note this does not mention anything about changing the definition of the table itself.