UTLRP cannot recompile "recompilable" objects

Hello,
I have a weird behaviour with utlrp; strange enough, I've discovered this recently although I use utlrp since years

test case: (Oracle 9.2.0.7)
as "SCOTT":
CREATE TABLE a( id NUMBER );
Table created.
CREATE TABLE b( id NUMBER );
Table created.
CREATE OR REPLACE VIEW ab AS
 SELECT a.id
   FROM a
   INNER JOIN b
     ON a.id =b.id;
View created.

Now we make the view invalid (by "touching" an underlying table)
ALTER TABLE b MODIFY( id NOT NULL );
Table altered.
SELECT status
  FROM user_objects
  WHERE object_name = 'AB'
    AND object_type = 'VIEW';
STATUS
-------
INVALID

Now, as SYS, I run "utlrp" to recompile all the invalid objects...