Now that I am at my desk I tested some stuff with your functions and I can't reproduce the issues you are seeing.

I did however make some adjustments to your scalar function that will make it a little faster and simpler.

Here is my proposed version.

CREATE FUNCTION [dbo].[fn_get_pst_datetime] (@serverdatetime datetime = NULL)

RETURNS datetime WITH SCHEMABINDING

AS

BEGIN

RETURN dateadd(hour, -1, ISNULL(@serverdatetime, GETDATE()))

END

Then here is the code I used to test:

CREATE TABLE testfunc (checkdate datetime)

--Checked designer here all is fine

INSERT INTO testfunc (checkdate)

SELECT dbo.fn_get_pst_datetime(DEFAULT)

--Checked designer here all is still fine

ALTER TABLE [dbo].[testfunc] ADD CONSTRAINT [DF_testfunc_checkdate] DEFAULT (dbo.fn_get_pst_datetime(DEFAULT)) FOR [checkdate]

--Checked designer here all is still fine

INSERT INTO testfunc (checkdate)

SELECT dbo.fn_get_pst_datetime(DEFAULT)

--Checked designer here all is still fine

Digging around the web it sounds like many people have run into the issue you are facing when there is a corrupt index on the base table. Obviously the table you posted here is an example and not the actual table you were having issues with.