pg_dumpall problems

Hi all,

Thanks for your help thus far. I almost have 8.2 ready (hooray no more
ancient 7.4). I do have one more problem which is likely the last thing
before pushing out live support. pg_dumpall isn't working.

Right now, we run pg_dumpall as a non-superuser, let's call it backup, whom
we give read access to the appropriate system tables (pg_shadow in 7.4,
pg_authid in 8.2), I get this error...
pg_dumpall: query failed: ERROR: permission denied for relation pg_authid
pg_dumpall: query was: SELECT rolname, rolsuper, rolinherit, rolcreaterole,
rolcreatedb, rolcatupdate, rolcanlogin, rolconnlimit, rolpassword,
rolvaliduntil, pg_catalog.shobj_description(oid, 'pg_authid') as rolcomment
FROM pg_authid ORDER BY 1

The weird thing is, whenever I run this exact same command from psql as the
backup user, it works.

template1=> select current_role;
current_user
--------------
backup
(1 row)
template1=> \z pg_catalog.pg_authid;
Access privileges for database "template1"
Schema | Name | Type | Access privileges
------------+-----------+-------+----------------------------------------------
pg_catalog | pg_authid | table |
{postgres=arwdxt/postgres,backup=r/postgres}

template1=> SELECT rolname, rolsuper, rolinherit, rolcreaterole,
rolcreatedb, rolcatupdate, rolcanlogin, rolconnlimit, rolpassword,
rolvaliduntil, pg_catalog.shobj_description(oid, 'pg_authid') as rolcomment
FROM pg_authid ORDER BY 1;
template1=> SELECT rolname, rolsuper, rolinherit, rolcreaterole,
rolcreatedb, rolcatupdate, rolcanlogin, rolconnlimit, rolpassword,
rolvaliduntil, pg_catalog.shobj_description(oid, 'pg_authid') as rolcomment
FROM pg_authid ORDER BY 1;
(There's data...glorious, glorious data).

The easy solution is to make backup a database superuser, but that's a
change I'd not like to make right now since I don't understand all the
security implications. What's the deal with this error, and is there any
nicer solution? Thanks much in advance.

Peter