Very puzzling sort behavior

Hi. In a table that includes these columns:

my_db=> \d tbl_client
...
name_last | character varying(40) | not null
name_first | character varying(30) | not null
...

I am extremely puzzled by the sorting of the "CLARKE"s in this list:

my_db=> SELECT name_last,length(name_last),name_last='CLARK' AS
clark,name_last='CLARKE' AS clarke FROM tbl_client WHERE name_last ILIKE
'CLARK%' OR name_last ILIKE 'ADAMS%' ORDER BY name_last || ', ' ||
name_first;
name_last | length | clark | clarke
-----------+--------+-------+--------
ADAMS | 5 | f | f
ADAMS | 5 | f | f
ADAMS | 5 | f | f
ADAMS | 5 | f | f
ADAMS | 5 | f | f
ADAMS | 5 | f | f
ADAMSON | 7 | f | f
CLARK | 5 | t | f
CLARK | 5 | t | f
CLARKE | 6 | f | t
CLARKE | 6 | f | t
CLARKE | 6 | f | t
CLARK | 5 | t | f
CLARK | 5 | t | f
CLARK | 5 | t | f
CLARK | 5 | t | f
CLARK | 5 | t | f
(17 rows)

The ADAMS are included just to show a similar example is ordering
correctly. I put the length and equality test columns in to try to make
sure there weren't some bizarre characters in the data. This is only
happening on one particular database. I did a reindex on the table just
for good measure. If I remove the name_first piece of the ORDER BY (which
doesn't seem like it should matter), it sorts as expected:

my_db=> SELECT name_last,length(name_last),name_last='CLARK' AS
clark,name_last='CLARKE' AS clarke FROM tbl_client WHERE name_last ILIKE
'CLARK%' OR name_last ILIKE 'ADAMS%' ORDER BY name_last || ', '

;
name_last | length | clark | clarke
-----------+--------+-------+--------
ADAMS | 5 | f | f
ADAMS | 5 | f | f
ADAMS | 5 | f | f
ADAMS | 5 | f | f
ADAMS | 5 | f | f
ADAMS | 5 | f | f
ADAMSON | 7 | f | f
CLARK | 5 | t | f
CLARK | 5 | t | f
CLARK | 5 | t | f
CLARK | 5 | t | f
CLARK | 5 | t | f
CLARK | 5 | t | f
CLARK | 5 | t | f
CLARKE | 6 | f | t
CLARKE | 6 | f | t
CLARKE | 6 | f | t
(17 rows)

I tried selecting those 17 rows from tbl_client into a new table, and get
the same odd behavior. However, if I run with new data I get an expected
order:

CREATE TEMP TABLE test (
name_first VARCHAR(40),
name_last VARCHAR(30)

);

INSERT INTO test VALUES ('JOE','CLARKE'),('BILL','CLARK');

SELECT * FROM test ORDER BY name_last;
SELECT * FROM test ORDER BY name_last || ', ' || name_first;

Any thoughts about what's going on, what to do about it, or what obvious
point I missing? Thanks in advance!

my_db=> SELECT version();
version

----------------------------------------------------------------------------------------------------------------
PostgreSQL 9.2.13 on x86_64-unknown-linux-gnu, compiled by gcc (GCC) 4.4.7
20120313 (Red Hat 4.4.7-11), 64-bit
(1 row)

Ken

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