Problem with BYTEA, CAST, and pg_dump

All,

I'm trying to use the crypt and decrypt functions from contrib and have
installed them into my database. The definition for crypt seems to
require that I use BYTEA datatype to input the data I need to encrypt.
All of my data is either TEXT or VARCHAR, though and not BYTEA.

I was trying to run a query like this from a trigger:

SELECT encrypt(NEW.card_number::bytea, 'password', 'bf')
INTO NEW.card_number_enc;

Problem is that a cast from VARCHAR to BYTEA didn't exist. I saw an
email thread that suggested I create the cast myself so I did:

CREATE CAST (VARCHAR TO BYTEA) WITHOUT FUNCTION;

And that worked. Now I can run the encrypt function above without a
problem.

However, when I use pg_dump and restore the dumped database, the CREAT
CAST is lost. Is this a bug with pg_dump or should I be doing something
different?

-- Dante