8.0.3 pg_autovacuum doesn't clear out stats table?

Hi,

I wonder if anyone can help me to identify why my background
pg_autovacuum doesn't appear to clear out the stats table entries?

Here is the non-commented lines in my postgresql.conf:

max_connections = 100
shared_buffers = 1000 # min 16, at least max_connections*2,
8KB each
vacuum_cost_delay = 10 # 0-1000 milliseconds
stats_start_collector = true
stats_row_level = true
lc_messages = 'C' # locale for system error message strings
lc_monetary = 'C' # locale for monetary formatting
lc_numeric = 'C' # locale for number formatting
lc_time = 'C' # locale for time formatting

And here is how I start pg_autovacuum:

# The PostgreSQL user is:
PGUSER=postgres

# LOG file is:
PG_AUTOVACUUM_LOG=/var/lib/postgresql/data/pg_autovacuum.log

# See the pg_autovacuum documentation for the details of how these
# parameters affect pg_autovacuum's aggressiveness.

VACUUM_BASE=1000
VACUUM_SCALE=2

SLEEP_BASE=300
SLEEP_SCALE=2

start-stop-daemon -o --chuid $PGUSER --start --quiet --exec
/usr/bin/pg_autovacuum -- -D -v $VACUUM_BASE -V $VACUUM_SCALE -s
$SLEEP_BASE -S $SLEEP_SCALE -L $PG_AUTOVACUUM_LOG

The problem I have is that pg_autovacuum doesn't appear to release the
unused space in the stats tables and so they grow without bounds. It
isn't clear to me that this is costing me anything other than disk
space, but when I run a vacuum full on the database it releases 2.5G of
space accumulated over about 9 months.

Most of my tables are update/append only (i.e. there are very few
deletions from the database), and the space does appear to belong to the
stats tables.

Is this a permissions or configuration issue, or does pg_autovacuum not
consider vacuuming of the stats tables?

Thanks in advance for any help you can offer me ...

Robin