pg_toast table growth out of control

I have a pg_toast table that is using up my entire storage device. When
I vacuum the database, it does not get smaller. This is driving me
crazy, since I have to dump and reload the data to shrink the database.

The table is simple:

rupert=# \d resp_body
Table "resp_body"
Column | Type | Modifiers
--------+---------+-----------
resp | integer | not null
body | text |
Unique keys: resp_body_resp_idx

The vacuum shows the problem:

rupert=# vacuum verbose resp_body;
NOTICE: --Relation resp_body--
NOTICE: Pages 1008: Changed 42, Empty 0; Tup 35101: Vac 0, Keep 0,
UnUsed 10292.
Total CPU 0.08s/0.03u sec elapsed 0.79 sec.
NOTICE: --Relation pg_toast_2947588--
NOTICE: Pages 1759978: Changed 555, Empty 0; Tup 197417: Vac 0, Keep 0,
UnUsed 6979775.
Total CPU 164.66s/9.69u sec elapsed 589.04 sec.
VACUUM

Hey, only 7 million unused records taking 15GB of disk, no problem!?!?

Help!

-jwb