the operator "=" does not work for some SQL queries

Harald Bartel (harald(dot)bartel(at)prozentor(dot)de) reports a bug with a severity of 2
The lower the number the more severe it is.

Short Description
the operator "=" does not work for some SQL queries

Long Description
Version: PostgreSQL 7.1
System: Debian Woody, both Linux 2.2.14 and 2.4.3

For some SQL queries (for an example see below) the operator "=" on text does not work, that is, no rows are returned, although some should be returned.In PostgreSQL 7.0.3 I avoided this problem by using
the LIKE operator instead of the "=" operator.In PostgreSQL 7.1 this
trick does not work anymore. But I found another way to avoid the problem by using SUBSTR. For example I used substr(text1,1,8)=substr(text2,1,8) instead of text1=text2 or
text1 like text2, where 8 is the length of both texts.

Sample Code
# original query that should work:

SELECT segment.nameenglischkurz, selektioneintrag_osi(transaktionh.selektion), wp.isin, unternehmen.namekurz FROM transaktionh, segment, wp, unternehmen, wpstamm WHERE wp.osi = selektioneintrag_osi(transaktionh.selektion) and wp.isin = wpstamm.isin and wpstamm.unternehmennr = unternehmen.unternehmennr and transaktionh.segmentnr = 43 and typnr = 3 and segment.segmentnr = transaktionh.segmentnr ORDER BY verkaufdt::datetime DESC;
nameenglischkurz | selektioneintrag_osi | isin | namekurz
------------------+----------------------+------+----------
(0 rows)

######################################
query using substr:

SELECT segment.nameenglischkurz, selektioneintrag_osi(transaktionh.selektion), wp.isin, unternehmen.namekurz FROM transaktionh, segment, wp, unternehmen, wpstamm WHERE substr(wp.osi,1,8) = substr(selektioneintrag_osi(transaktionh.selektion),1,8) and wp.isin = wpstamm.isin and wpstamm.unternehmennr = unternehmen.unternehmennr and transaktionh.segmentnr = 43 and typnr = 3 and segment.segmentnr = transaktionh.segmentnr ORDER BY verkaufdt::datetime DESC;
nameenglischkurz | selektioneintrag_osi | isin | namekurz
------------------+----------------------+--------------+------------------
DAX | DE710000 | DE0007100000 | DaimlerChrysler
DAX | DE604843 | DE0006048432 | Henkel
...

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