database error xx000?

I am doing a ton of pgsql over here defining and redefining functions and
triggers and every day or so I get this:

Error: Database error XX000: cache lookup failed for type 5276542
>
> Query: select dcm.task_user_dispos(42895::bigint, 870::bigint)
>
> [condition type: internal-error]
>
>
If I exit everything and start over (but not bouncing the PG server) the
problem goes away.

I gather this kind of DB error is not a user error, but I would still be
interested in learning how to avoid it because even in production we will
need to be redefining functions periodically.

Does the above give anyone any ideas at all about what is going on?

Environemnt is:

Version string PostgreSQL 9.1.2 on x86_64-unknown-linux-gnu, compiled by
> gcc (GCC) 4.4.5 20110214 (Red Hat 4.4.5-6), 64-bit

Thx, ken