Cache lookup failure for pg_restore?

After I restore a Postgres database (using pg_restore), I get the
following error message when I try to run a simple UPDATE query:

ERROR:  cache lookup failed for function 70529

More details:

1. I backup the database:

pg_dump -Fc --username=webclient [dbname] > database.backup

2. I restore the database:

dropdb -U postgres [dbname]
createdb -U postgres [dbname]
createlang -U postgres plpgsql [dbname]
pg_restore -v -U postgres -Fc -d [dbname] database.backup

3. I connect to the database and run a query:

$ psql cspan webclient
Welcome to psql 7.4, the PostgreSQL interactive terminal.

Type:  \copyright for distribution terms
       \h for help with SQL commands
       \? for help on internal slash commands
       \g or terminate with semicolon to execute query
       \q to quit

cspan=> update contact set gender = 'M';
ERROR:  cache lookup failed for function 70529

If I re-run the update, I get:

cspan=> update contact set gender = 'M';
server closed the connection unexpectedly
        This probably means the server terminated abnormally
        before or while processing the request.
The connection to the server was lost. Attempting reset: Failed.
!>

Any ideas what might be happening here? This is all running on a
RedHat linux box. The original database (before backup/restore) works
fine. The database has a few GIST (full-search, tsearch2) indices, but
otherwise is pretty ordinary.

Thanks in advance for any insight,

Razvan.