Backup to Tape Incomplete

PostgreSQL 8.2.4
RedHat ES4

I have a nightly cron job that is (supposed) to dump a specific database to
magnetic tape:
/usr/local/bin/pg_dump dbname > /dev/st0

This runs, and doesn't throw any errors, but when I try to restore it fails
because the tape is incomplete:
[postgres(at)stirling ~]$ cat /dev/st0 | tail


--
-- Name: rewards_points; Type: ACL; Schema: public; Owner: dbname
--

REVOKE ALL ON TABLE rewards_points FROM PUBLIC;
REVOKE ALL ON TABLE rewards_points FROM dbname;
GRANT ALL ON TABLE rewards_points TO dbname;
GRANT SELECT,INSERT,UPDATE ON TABLE rewards_points TO
PUBL[postgres(at)stirling ~]$

As you can see, the "end of file" is half-way through a SQL statement, and
doesn't even have a new-line marker.

The database is not too big for the tape - it's a DDS-3 tape drive (12/24gb)
and the database is not even 1gb:
[postgres(at)stirling ~]$ pg_dump dbname > /tmp/dbname080225.sql
[postgres(at)stirling ~]$ ls -lh /tmp/dbname080225.sql
-rw-r--r-- 1 postgres root 957M Feb 25 13:42 /tmp/dbname080225.sql

Is this a PostgreSQL issue or a tape drive issue? I can use tar to read and
write without any problems.

Do I need to change the block size on the tape drive?

[phillips(at)stirling ~]$ mt stat
SCSI 2 tape drive:
File number=0, block number=0, partition=0.
Tape block size 512 bytes. Density code 0x25 (DDS-3).
Soft error count since last status=0
General status bits on (41010000):
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