SQL Server bug set: "user-defined functions and group"

/** = ** 1. An error occurred while using the custom function for group by. ** = **/
-- A simple function
Create Function f_str (@ STR sysname, @ I INT)
Returns char (1)
As begin
Return (substring (@ STR, @ I, 1 ))
End
Go

-- Below is the test

-- Define test data
Declare @ t table (name sysname)
Insert into @ T values ('abcd ')

-- If group by exists, the result is incorrect.
Select a = DBO. f_str (name, 1), B = DBO. f_str (name, 2)
From @ t
Group by DBO. f_str (name, 1), DBO. f_str (name, 2)

-- The result is correct if no group by exists.
Select a = DBO. f_str (name, 1), B = DBO. f_str (name, 2)
From @ t
Go

-- Delete the User-Defined Function
Drop function f_str

/* -- Test Result
A B
--------
A

(The number of affected rows is 1)

A B
--------
A B

(The number of affected rows is 1)
--*/