BUG #5622: Query failed: server closed the connection unexpectedly

The following bug has been logged online:

Bug reference: 5622
Logged by: Thue Janus Kristensen
Email address: thuejk(at)gmail(dot)com
PostgreSQL version: 8.4.4
Operating system: Ubuntu 10.04 LTS i386
Description: Query failed: server closed the connection unexpectedly
Details:

I have a 100% reproducible server crash with postgresql. This crash does not
happen on my 8.3 installation.

When the crash occurs I get
pg_query(): Query failed: server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.

However, I have been unable to simplify the error condition :(. I tried
dumping 8000 lines of sql, but when I run them separately, I don't get a
crash.

The last lines before the crash are ($db->query is a prepared query,
$db->simple_query is a non-prepared query):
<?php
$db->query("SAVEPOINT lala");
$res = questions::move_question($t->e, $g1q1_id, $g2_id); //some queries
here
$db->query("ROLLBACK TO SAVEPOINT lala");
$db->query("RELEASE SAVEPOINT lala");
//some queries here
$res = aas::insert_in_group($t->e, $aa_id, $g2_id);
$res = questions::move_question($t->e, $g1q1_id, $g2_id);
//crash when line below is run!
$db->simple_query("SET CONSTRAINTS ALL IMMEDIATE");
?>

/var/log/syslog:
Aug 17 23:08:26 thue-laptop kernel: [46188.626357] postgres[11461]: segfault
at 21723858 ip 00772286 sp bf8a4a80 error 4 in postgres[621000+446000]

/var/log/postgresql/postgresql-8.4-main.log
2010-08-17 23:08:26 CEST LOG: server process (PID 11461) was terminated by
signal 11: Segmentation fault
2010-08-17 23:08:26 CEST LOG: terminating any other active server
processes
2010-08-17 23:08:26 CEST WARNING: terminating connection because of crash
of another server process
2010-08-17 23:08:26 CEST DETAIL: The postmaster has commanded this server
process to roll back the current transaction and exit,\
because another server process exited abnormally and possibly corrupted
shared memory.
2010-08-17 23:08:26 CEST HINT: In a moment you should be able to reconnect
to the database and repeat your command.
2010-08-17 23:08:26 CEST LOG: all server processes terminated;
reinitializing
2010-08-17 23:08:26 CEST LOG: database system was interrupted; last known
up at 2010-08-17 23:04:02 CEST
2010-08-17 23:08:26 CEST LOG: database system was not properly shut down;
automatic recovery in progress
2010-08-17 23:08:26 CEST LOG: redo starts at 0/37500054

I realize that this is probably not enough to understand the bug, but I will
be happy to try to debug it further, if I am given a pointer as to how.