Update documentation on GRANT SCEMA USAGE, again.

doc/src/sgml/ref/grant.sgml

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-$PostgreSQL: pgsql/doc/src/sgml/ref/grant.sgml,v 1.58 2006/07/19 18:42:31 momjian Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/grant.sgml,v 1.59 2006/07/20 18:00:03 momjian Exp $
 PostgreSQL documentation
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@@ -276,8 +276,10 @@ GRANT <replaceable class="PARAMETER">role</replaceable> [, ...]
        schema (assuming that the objects' own privilege requirements are
        also met).  Essentially this allows the grantee to <quote>look up</>
        objects within the schema.  Without this permission, it is still
-       possible to see the object names, e.g. by querying the system tables,
-       so this is not a completely secure way to prevent object access.
+       possible to see the object names, e.g. by querying the system tables.
+       Also, after revoking this permission, existing backends might have
+       statements that have previously performed this lookup, so this is not
+       a completely secure way to prevent object access.
       </para>
       <para>
        For sequences, this privilege allows the use of the