Order by "Alias Name"

We have this query:

create table testme11
(id int identity(1,1),
source_name varchar(20),
source_description varchar(20))

insert into testme11 values ('A',NULL)
insert into testme11 values (NULL,'Q')
insert into testme11 values ('E',NULL)
insert into testme11 values (NULL,'C')

select * from testme11
id source_name source_description
----------- -------------------- --------------------
1 A NULL
2 NULL Q
3 E NULL
4 NULL C

(4 row(s) affected)


Are this three queries will return the same result?
A.
SELECT id,ISNULL(source_name,source_description) AS source_name
FROM testme11 src
order by src.source_name

B.
SELECT id,ISNULL(source_name,source_description) AS source_name
FROM testme11 src
order by source_name

C.
SELECT id,ISNULL(source_name,source_description) AS source_name
FROM testme11 src
order by ISNULL(source_name,source_description)

result A:
id source_name
----------- --------------------
2 Q
4 C
1 A
3 E
(4 row(s) affected)

result B:
id source_name
----------- --------------------
1 A
4 C
3 E
2 Q

(4 row(s) affected)


Result C:
id source_name
----------- --------------------
1 A
4 C
3 E
2 Q

(4 row(s) affected)

Query B & C will return same result, while Query A won't return expected result