FreeBSD problem under heavy load

I seem to run into a serious problem. With 6.5.x + FreeBSD 3.2, I get
a core under heavy load (16 or more concurrent users). FreeBSD 2.2.x
seems more stable but soon or later same thing happens. Examing a
core, I found it segfaulted in hash_search(). It was not possible to
get more info having a -g compiled backend becasue it did not fail if -
g was given. It is likely that random memory corruptions occured. It
is also reported by a user that he often sees:

NOTICE: LockReplace: xid table corrupted

Note that these problems never happen on Linux (even running 128 users
are ok on Linux). Only FreeBSD is suffered as far as I can see(not
sure about other *BSD). Increasing shmem or semaphore never helps.

How to reproduce the problem:

1) obtain pgbench source from
ftp.sra.co.jp/pub/cmd/postgres/pgbench/pgbench-1.1.tar.gz

2) unpack the archive and run configure

3) edit the first line in Makefile

POSTGRESHOME = /usr/local/pgsql

4) make. you will get an executable "pgbench" there.

5) make a fresh DB (suppose it is "test")

6) initialize DB

pgbench -i test

this will take for a while

7) run the test

pgbench -n -c numeber_of_concurrent users test

I see problems with numeber_of_concurrent users ~ 16 or more.

Here are my shmem settings:

shminfo:
shmmax: 41943041 (max shared memory segment size)
shmmin: 1 (min shared memory segment size)
shmmni: 32 (max number of shared memory identifiers)
shmseg: 8 (max shared memory segments per process)
shmall: 10240 (max amount of shared memory in pages)

seminfo:
semmap: 40 (# of entries in semaphore map)
semmni: 32 (# of semaphore identifiers)
semmns: 256 (# of semaphores in system)
semmnu: 30 (# of undo structures in system)
semmsl: 256 (max # of semaphores per id)
semopm: 100 (max # of operations per semop call)
semume: 10 (max # of undo entries per process)
semusz: 92 (size in bytes of undo structure)
semvmx: 32767 (semaphore maximum value)
semaem: 16384 (adjust on exit max value)

Any thoughts?
--
Tatsuo Ishii