Bug #894: different result with the same parameterlist in function call

Kovacs Balazs (balazs(dot)kovacs(at)jonapot(dot)hu) reports a bug with a severity of 3
The lower the number the more severe it is.

Short Description
different result with the same parameterlist in function call

Long Description
I have written a simple function in C under pg (it uses regex lib):
#include <stdio.h>
#include <string.h>
#include <regex.h>
#include <postgres.h>
#include <fmgr.h>

PG_FUNCTION_INFO_V1(crightevaledge);
Datum crightevaledge(PG_FUNCTION_ARGS)
{
text *pattern = (text*)PG_GETARG_TEXT_P(0);
text *sample = (text*)PG_GETARG_TEXT_P(1);
char *char_pattern = (char*)VARDATA(pattern);
char *char_sample = (char*)VARDATA(sample);
regex_t compre_pattern;
int32 retval;

if (regcomp(&compre_pattern,char_pattern,0)!=0) PG_RETURN_INT32(2);
if (regexec(&compre_pattern,char_sample,0,NULL,0)==0) retval=1;
else retval=0;
regfree(&compre_pattern);
PG_RETURN_INT32(retval);
}

I compile it:
gcc -fpic -c -I/usr/local/postgresql-7.2.1/src/include -I/usr/local/pgsql/include sample.c
gcc -shared -o sample.so sample.o

and create a function under pg:
create function crightevaledge(text,text) returns int4 as '/devel/pg/sample.so' language 'C';

I have created a simple table for test, like this (in an empty database (named test)):
create table test(descr text,
path text);

I put into it some records:
insert into test values('test1','test1.dat');
insert into test values('test2','test2.mpg');
insert into test values('test3','test3.pdf');

After, i executed the following query more than 1 times:
select descr,crightevaledge('.*mpg',path) from test;
The result was different on different executing:

test=# select descr,crightevaledge('.*mpg',path) from test;
descr | crightevaledge
-------+----------------
test1 | 0
test2 | 0
test3 | 0
(3 rows)

test=# select descr,crightevaledge('.*mpg',path) from test;
descr | crightevaledge
-------+----------------
test1 | 0
test2 | 1
test3 | 0
(3 rows)

test=# select descr,crightevaledge('.*mpg',path) from test;
descr | crightevaledge
-------+----------------
test1 | 0
test2 | 0
test3 | 0
(3 rows)

test=# select descr,crightevaledge('.*mpg',path) from test;
descr | crightevaledge
-------+----------------
test1 | 0
test2 | 1
test3 | 0
(3 rows)

I use postgres 7.2.1 version, and redhat 7.2 (with kernel 2.4.20).

Sample Code

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