Polymorphic functions' weird behavior

[Viatcheslav Kalinin <vka(at)ipcb(dot)net>]

Hello
We've come across  the following issue with Polymorphic functions:

CREATE OR REPLACE FUNCTION "array_to_set" (vaarray anyarray) RETURNS 
SETOF anyelement AS
$body$
BEGIN
  FOR I IN COALESCE(ARRAY_LOWER(VAARRAY, 1), 1) .. 
COALESCE(ARRAY_UPPER(VAARRAY, 1), 0) LOOP
      RETURN NEXT VAARRAY[I];
  END LOOP;
END
$body$
LANGUAGE 'plpgsql' SECURITY INVOKER;


> select * from array_to_set(array[1,2,3]);
array_to_set
--------------
          1
          2
          3
(3 rows)


Now we change SECURITY INVOKER clause to SECURITY DEFINER and voila:

> select * from array_to_set(array[1,2,3]);
ERROR:  could not determine actual argument type for polymorphic 
function "array_to_set"

Though explainable this is absolutely strange since logically security 
rules and polymorphism are irrelevant.

regards, Viatcheslav