Bug in sortin routine?

Hello everyone,
I am not sure if this is the appropriate mailing lists. But lets try
anyway.
It seems that the sorting order on dates is incorrect under certain
circumstances:
The query :
select tdat
from   quick
where empfang like 'HUK-COBURG VERS.-GRUPPE' and
      zweck like 'BEITRAG F. 300/338958-M    PFLEGEPFLICHTVERSICHERUNG'
      and date_part ('year',tdat::datetime)=1997
      order by tdat;
produces:
      tdat
----------
1997-01-04
1997-01-08
1997-01-09
1997-01-10
1997-01-12
1997-02-01
1997-02-05
1997-02-06
1997-02-07
1997-03-02
1997-03-03
1997-03-11
(12 rows)

while this gives the correct sort order:

select tdat
from   quick
  order by tdat;

1997-11-26
1997-11-27
1997-11-27
1997-11-27
1997-11-28
1997-11-28
1997-11-28
1997-12-03
1997-12-05
1997-12-05         (just a section)

any idea of what may be going on?
set DateStyle to 'German'; (does not have an effect on the problem)
postgresql-6.4.2-2
readhat 5.2

greetings

Eildert Groeneveld

=========================================
Institute for
Animal Science and Animal Behaviour
Mariensee 31535 Neustadt Germany
Tel   : (49)(0)5034 871155
Fax   : (49)(0)5034 92579
www   : http://www.tzv.fal.de/~eg/
e-mail: eg@tzv.fal.de
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