reuse sysids security hole?

(Thought triggered by something Tom said the other day)

Is this a security hole? Looks like one to me. Would it be better to use
a sequence generator for sysids instead of using max+1 on the user
table? Or else store the last sysid used somewhere?

andrew

facetest=# create user blurfl;
CREATE USER
facetest=# create table blurfltable (a text, b text);
CREATE TABLE
facetest=# alter table blurfltable owner to blurfl;
ALTER TABLE
facetest=# drop user blurfl;
DROP USER
facetest=# create user floobl;
CREATE USER
facetest=# \dt blurfltable
List of relations
Schema | Name | Type | Owner
--------+-------------+-------+--------
public | blurfltable | table | floobl
(1 row)

facetest=#