Segmentation fault.

I've got a MSAccess client application. The application use ODBC to connect
to server.
Such as in my queries clauses like "some_boolean = TRUE" converts to
"some_boolean = 1",
I have to create a server procedure:
CREATE FUNCTION is_bool_eq_int(BOOL,INT4) RETURNS BOOL AS '
DECLARE
sec BOOL;
BEGIN
IF $2 = 0 THEN
sec = ''f'';
ELSE
sec = ''t'';
END IF;
RETURN ($1 = sec);
END;
' LANGUAGE 'plpgsql';

CREATE OPERATOR = (
PROCEDURE = is_bool_eq_int,
LEFTARG = BOOL,
RIGHTARG = INT4,
COMMUTATOR = '=',
NEGATOR = '!=',
RESTRICT = eqsel,
JOIN = eqjoinsel
);
All works fine. But one query fails when I use search on boolean field.

Here is backtrace.
===============================================================
[nedvigimost2]# gdb /usr/local/pgsql-7.0.2/bin/postgres ./core
GNU gdb 4.17.0.4 with Linux/x86 hardware watchpoint and FPU support
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GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain
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Type "show copying" to see the conditions.
There is absolutely no warranty for GDB. Type "show warranty" for details.
This GDB was configured as "i386-redhat-linux"...

warning: core file may not match specified executable file.
Core was generated by `/usr/local/pgsql/bin/postgres 192.168.1.67 an'.
Program terminated with signal 11, Segmentation fault.
Reading symbols from /lib/libcrypt.so.1...done.
Reading symbols from /lib/libnsl.so.1...done.
Reading symbols from /lib/libdl.so.2...done.
Reading symbols from /lib/libm.so.6...done.
Reading symbols from /lib/libutil.so.1...done.
Reading symbols from /usr/lib/libreadline.so.3...done.
Reading symbols from /lib/libtermcap.so.2...done.
Reading symbols from /usr/lib/libncurses.so.4...done.
Reading symbols from /lib/libc.so.6...done.
Reading symbols from /lib/ld-linux.so.2...done.
Reading symbols from /lib/libnss_files.so.2...done.
Reading symbols from /usr/local/pgsql/lib/plpgsql.so...done.
#0 0x80a3ff0 in ExecEvalExpr ()
(gdb) bt
#0 0x80a3ff0 in ExecEvalExpr ()
#1 0x80ac0e8 in ExecSubPlan ()
#2 0x80a414f in ExecEvalExpr ()
#3 0x80a41be in ExecQual ()
#4 0x80a4649 in ExecScan ()
#5 0x80a7fd3 in ExecIndexScan ()
#6 0x80a2da9 in ExecProcNode ()
#7 0x80a93db in ExecNestLoop ()
#8 0x80a2dba in ExecProcNode ()
#9 0x80a93a1 in ExecNestLoop ()
#10 0x80a2dba in ExecProcNode ()
#11 0x80a93a1 in ExecNestLoop ()
#12 0x80a2dba in ExecProcNode ()
#13 0x80a93a1 in ExecNestLoop ()
#14 0x80a2dba in ExecProcNode ()
#15 0x80a1f2d in ExecutePlan ()
#16 0x80a144e in ExecutorRun ()
#17 0x81003d4 in ProcessQueryDesc ()
#18 0x8100461 in ProcessQuery ()
#19 0x80fecbc in pg_exec_query_dest ()
#20 0x80feb82 in pg_exec_query ()
#21 0x80ffd33 in PostgresMain ()
#22 0x80e8072 in DoBackend ()
#23 0x80e7c40 in BackendStartup ()
#24 0x80e6e49 in ServerLoop ()
#25 0x80e681e in PostmasterMain ()
#27 0x401069ab in __libc_start_main (main=0x80b2cf0 <main>, argc=8,
argv=0xbffffbb4, init=0x80645c8 <_init>, fini=0x8145984 <_fini>,
rtld_fini=0x4000ad00 <_dl_fini>, stack_end=0xbffffbac)
at ../sysdeps/generic/libc-start.c:92
(gdb)