pg_clog not getting cleared

Hello. I posted this once before, but I'm encountering it again.

Each Saturday, I run: vacuumdb -a -v. I have autovac on all the time.

However, my pg_clog directory lists clog files going back to July.

This is pg 8.4.4 on Linux (CentOS 5.5).

I know this isn't a whole lot of information at this time. What more would be useful in finding out what's failing and where?

I seem to recall that doing vacuumdb -f -a -v resolved it, which would seem to point to a database not being vacuumed, but that's sort of the point of the -a switch, right? I'm running this as the "postgres" user himself.