BUG #5344: pg_restore some foreign keys missing

The following bug has been logged online:

Bug reference: 5344
Logged by: Simon Ng
Email address: simon94086(at)yahoo(dot)com
PostgreSQL version: 8.1.11
Operating system: RedHat Linux
Description: pg_restore some foreign keys missing
Details:

from server1 with Postgres 8.1.11 on RedHat Linux
pg_dump -C -f db1.tar.gz -F c -Z5 -U postgres db1

copy db1.tar.gz over to server2 with Postgres 8.1.11 on RedHat Linux
drop database db1;
pg_restore -C -d template1 -h localhost -U postgres db1.tar.gz
the database of db1 is restored but the schema is incomplete. Some tables
have the proper foreign keys but some tables don't.

copy the same db1.tar.gz from server1 to a Win XP machine with Postgres 8.4
drop database db1;
pg_restore -C -d template1 -h localhost -U postgres db1.tar.gz
Those tables that have missing foreign keys in server2 do have the proper
foreign
keys defined.

server1 and server2 have the same version of OS and same version of
Postgres.
Why are some foreign keys missing during the restore?