Upgrade to 9.1 causing function problem

I have recently upgraded my database from 8.4 to 9.1.  In the process I have moved everything to a different schema.
Postgisis occupying the public schema.  Everything is working fine except for some of my own functions. Here is a small
functionand table that will not update when I perform the following code:    select
_me_set_process_month('2012-01-01');    It will run but the resulting table will not update.  Any ideas? 


CREATE OR REPLACE FUNCTION _me_set_process_month(date)
  RETURNS void AS
$BODY$

BEGIN

update activity_month set action_month = $1;


END;
$BODY$
  LANGUAGE plpgsql VOLATILE
  COST 100;
ALTER FUNCTION _me_set_process_month(date)
  OWNER TO postgres;



CREATE TABLE activity_month
(
  action_month date NOT NULL,
  CONSTRAINT idkeymonth PRIMARY KEY (action_month )
)
WITH (
  OIDS=FALSE
);
ALTER TABLE activity_month
  OWNER TO postgres;
GRANT ALL ON TABLE activity_month TO public;
GRANT ALL ON TABLE activity_month TO postgres;