blocking referencing system catalogs in 8.4 breaks my code

In testing my software on postgresql-8.4beta[12] I got
   ERROR:  42501: permission denied: "pg_namespace" is a system catalog   LOCATION:  ATAddForeignKeyConstraint,
tablecmds.c:4599

from my code which has a column   schema_name name NOT NULL REFERENCES pg_namespace ON DELETE CASCADE

this despite PostgreSQL happily accepting:   GRANT REFERENCES ON pg_namespace TO greg;

I found the change in tablecmds.c and a mention of it in PostgreSQL
Weekly News - May 17 2009, yet I don't understand why referencing
a system table in this manner should be a problem - is it?

I'm trying to have certain rows of my tables go away if certain
schemas are dropped.  Is there a preferred way to do this?

If this regression is retained, it needs to be documented in the
reference manual AND I think that an attempt to GRANT REFERENCES
privileges to a system table should not be allowed.

BTW, I'm loving most of what I see in 8.4,

_Greg

J. Greg Davidson