Custom types and pg_dump

A quick request for a pointer to look or an answer.

Background:

I was asked to test the results of a pg_dump of a database.

While and after doing a import ("\i file_dump") I notice one table had
two attributes with a type of "unknown". I'm not sure of the Pg version
it cam from but I was putting it into an 8.3.6 database from the PGDG
yum repo on a CentOS 5.2 system.

So the question is; is it possible to have a custom type in a cluster
that is accessible/usable in a database but isn't picked up by pg_dump?

Again a pointer of where to look would be fine. (I've never seen this
mentioned, not that is unusual for me, in the pg_dump documentation.)

TIA,
Rod
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