IMMUTABLE bug ?

I cant get the IMMUTABLE modifier meaning.

The 'testme' IMMUTABLE function is invoked 3 times 
in the following query:
 # select testme(1), testme(1), testme(1); NOTICE:  called NOTICE:  called NOTICE:  called  testme | testme | testme
--------+--------+-------- ret    | ret    | ret (1 row)
 

Why is so ? shouldn't the IMMUTABLE keywork make
it a single call ?


From the 8.0 manual :
 IMMUTABLE indicates that the function always returns the same result when given the same argument values; that is, it
doesnot do database lookups or otherwise use information not directly present in its argument list. If this option is
given,any call of the function with all-constant arguments can be immediately replaced with the function value.
 

The function definition:

 CREATE OR REPLACE FUNCTION testme(integer) RETURNS text AS ' BEGIN         RAISE NOTICE ''called'';         return
''ret''::text;END ' LANGUAGE 'plpgsql' IMMUTABLE STRICT;
 


PostgreSQL version 8.0.0



--strk;