sql command strange behaviour

Hello the list

I have a problem with an sql command and I not understand what is happens.
I execute this query and the result is ok :

db_stats=# SELECT code, label, typecumul FROM table_f801_cat_period
INNER JOIN table_cat_period USING (code) WHERE typecumul = 0 EXCEPT
SELECT code_base, label, typecumul FROM (SELECT code_base FROM
table_cat_period_tcodes INNER JOIN table_f801_cat_period ON
(code_cumul=code)) AS orphan_f801 INNER JOIN table_cat_period ON
(code_base=code) ORDER BY code;
code | label | typecumul
----------+----------+-----------
20080799 | Jul 2008 | 0
(1 ligne)

db_stats=#

Now I execute this query that request one column more, the "ind" field.,
the return of this query is bad.

db_stats=# SELECT code, label, typecumul, ind FROM table_f801_cat_period
INNER JOIN table_cat_period USING (code) WHERE typecumul = 0 EXCEPT
SELECT code_base, label, typecumul, ind FROM (SELECT code_base, ind FROM
table_cat_period_tcodes INNER JOIN table_f801_cat_period ON
(code_cumul=code) AND (ind=ind)) AS orphan_f801 INNER JOIN
table_cat_period ON (code_base=code) ORDER BY ind, code;
code | label | typecumul | ind
----------+----------+-----------+-----
20040199 | Jan 2004 | 0 | 0
20040299 | Feb 2004 | 0 | 1
20040399 | Mar 2004 | 0 | 2
20040499 | Apr 2004 | 0 | 4
20040599 | May 2004 | 0 | 5
20040699 | Jun 2004 | 0 | 6
20040799 | Jul 2004 | 0 | 9
20040899 | Aug 2004 | 0 | 10
20040999 | Sep 2004 | 0 | 11
20041099 | Oct 2004 | 0 | 13
20041199 | Nov 2004 | 0 | 14
20041299 | Dec 2004 | 0 | 15
20050199 | Jan 2005 | 0 | 19
20050299 | Feb 2005 | 0 | 20
20050399 | Mar 2005 | 0 | 21
20050499 | Apr 2005 | 0 | 23
20050599 | May 2005 | 0 | 24
20050699 | Jun 2005 | 0 | 25
20050799 | Jul 2005 | 0 | 28
20050899 | Aug 2005 | 0 | 29
20050999 | Sep 2005 | 0 | 30
20051099 | Oct 2005 | 0 | 32
20051199 | Nov 2005 | 0 | 33
20051299 | Dec 2005 | 0 | 34
20060199 | Jan 2006 | 0 | 38
20060299 | Feb 2006 | 0 | 39
20060399 | Mar 2006 | 0 | 40
20060499 | Apr 2006 | 0 | 42
20060599 | May 2006 | 0 | 43
20060699 | Jun 2006 | 0 | 44
20060799 | Jul 2006 | 0 | 47
20060899 | Aug 2006 | 0 | 48
20060999 | Sep 2006 | 0 | 49
20061099 | Oct 2006 | 0 | 51
20061199 | Nov 2006 | 0 | 52
20061299 | Dec 2006 | 0 | 53
20070199 | Jan 2007 | 0 | 57
20070299 | Feb 2007 | 0 | 58
20070399 | Mar 2007 | 0 | 59
20070499 | Apr 2007 | 0 | 61
20070599 | May 2007 | 0 | 62
20070699 | Jun 2007 | 0 | 63
20070799 | Jul 2007 | 0 | 66
20070899 | Aug 2007 | 0 | 67
20070999 | Sep 2007 | 0 | 68
20071099 | Oct 2007 | 0 | 70
20071199 | Nov 2007 | 0 | 71
20071299 | Dec 2007 | 0 | 72
20080199 | Jan 2008 | 0 | 76
20080299 | Feb 2008 | 0 | 77
20080399 | Mar 2008 | 0 | 78
20080499 | Apr 2008 | 0 | 80
20080599 | May 2008 | 0 | 81
20080699 | Jun 2008 | 0 | 82
20080799 | Jul 2008 | 0 | 85
(55 lignes)

db_stats=#

if anyone have an idea ...

Thanks in advance

Guy