recursive query returning extra rows in 8.4

Hi all,

Using postgres 8.4.13 (latest that redhat provides in rhel6) the query
below returns an extra row compared to running the same thing in later
versions (tried 9.0, 9.1, 9.2 - they don't return the extra row).

Just wondering if anyone had thoughts on why, and/or how to remove the
duplicate row. It gets worse the more rows in the initial 'data' section.

WITH RECURSIVE data AS
(
SELECT CAST('/a/' AS TEXT) AS path, CAST(1 AS INTEGER) AS depth
UNION ALL
SELECT '/a/a/', 2
),
numbers AS
(
SELECT path, depth AS iteration, depth AS depth, 'A'
FROM data
WHERE depth =
(
SELECT MIN(depth)
FROM data
)
UNION ALL
(
WITH sub_sumbers AS
(
SELECT path, (iteration + 1) AS iteration, depth
FROM numbers
WHERE iteration <
(
SELECT MAX(depth)
FROM data
)
)
SELECT path, iteration, depth, 'b'
FROM sub_sumbers
UNION ALL
SELECT path, depth, depth, 'c'
FROM data
WHERE depth =
(
SELECT MAX(iteration)
FROM sub_sumbers
)
)
)
SELECT *
FROM numbers
ORDER BY iteration, depth;

path | iteration | depth | ?column?
-------+-----------+-------+----------
/a/ | 1 | 1 | A
/a/ | 2 | 1 | b
/a/ | 2 | 1 | b
/a/a/ | 2 | 2 | c
(4 rows)

The 'b' row is duplicated (but not in later versions of postgres).

Thanks for any suggestions/advice.

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