pg_restore problem

I have a problem restoring our large database. This has only stared
happening since we moved to 8.1.x

We are currently on 8.1.3.

We perform an over night dump of the database as follows;

pg_dump -Ft $db | bzip2 > $db.dump.tbz

This happens fine, without any errors.

On our backup machine also running 8.1.3 we do the following;

createdb $db
bzip2 -d -c $db.dump.tbz | pg_restore -i -O -d $db

However, after a while we get this error;

pg_restore: [tar archiver] could not find header for file 3765.dat in
tar archive

Our bzip2ed database is 1.2G so it's not small. We also run the same
procedure on a number of other smaller database and have no problems at
all. However, we are now in the unhandy position of having our main
operational database that we can backup, but not restore!

Help.