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. Postgis is occupying the public schema. Everything is working fine except for some of my own functions. Here is a small function and 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;