Error: missing chunk number ...

Hi,

I've recently observed some strange behavior using postgresql 7.2.1 on a 
RH-7.3 system. I've got a service for fetching rss feeds from the web. 
These feeds are stored into a text column. Here's how the table looks like:
    Column      |           Type           | Modifiers
------------------+--------------------------+-----------
channel_id       | integer                  |
dataurl          | character varying(1000)  |
...
...
latest_feed      | text                     |
feedidx          | txtidx                   |
Indexes: hellofeedidx

(feedidx uses tsearch and indexes the faulty column, namely latest_feed).

This is not on a production system. After running this service for a 
while (almost a week). I get messages like:

# select * from rss_channels;
ERROR:  missing chunk number 1 for toast value 797979

If I try to delete the culprit row. I get:
# delete from rss_channels where channel_id=116;
ERROR:  simple_heap_delete: tuple already updated by self

I'm running a full vacuum daily:
su - postgres -c 'vacuumdb --full --analyze --quiet --all'

and a simple vacuum once every hour:
su - postgres -c 'vacuumdb --analyze --quiet --all'

Here's how I configure and run PG:
./configure --enable-multibyte=UNICODE --with-tcl --with-perl 
--enable-syslog

su -l postgres -c 'export LANG=C; /usr/local/pgsql/bin/postmaster -N 200 
-B 1000 -o "-S 2000" -S -D /usr/local/pgsql/data '


Note that I cannot do a pg_dump on the rss_channels table.

Any idea of what might be the problem?

Best wishes,
Neophytos