pg_archivecleanup not cleaning up ?

Running Postgres 9.2.4 on centos 6

We have a backup script that runs twice weekly. At the end of the script it
executes a pg_archivecleanup to remove the old WAL files no longer needed.

Most of the time this runs as expected. But for some reason, it does not
cleanup ALL of the old wal files.

I noticed today that I still had 3500 wal files. I ran the command
manually, and the screen scrolled by with its usual removing file message.

Afterwards, I did an ls | wc - l only to see it had only removed a few. In
the end, I had to run the same pg_archivecleanup about 5 times in order to
remove all of the old wal files.

Is there a known issues with this command?

Here is the command I ran.

pg_archivecleanup -d /opt/dbbackups/db1_wal_keep
000000010000002200000049.00000020.backup

--
Thanks,

Jorge Torralba
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