FOUND not set by EXECUTE?

I had expected the FOUND PL/pgSQL variable to be set by an UPDATE
statement executed by an EXECUTE statement, but it doesn't appear to
work:

try=# drop table try;
DROP TABLE
try=# CREATE TABLE try (
try(# id integer
try(# );
CREATE TABLE
try=# INSERT INTO try VALUES (1);
INSERT 0 1
try=# CREATE OR REPLACE FUNCTION try_me () RETURNS VOID AS $$
try$# DECLARE
try$# rcount integer;
try$# BEGIN
try$# EXECUTE 'UPDATE try SET ID = 12';
try$# RAISE NOTICE 'Found: %', FOUND;
try$# GET DIAGNOSTICS rcount = ROW_COUNT;
try$# RAISE NOTICE 'Row Count: %', rcount;
try$# END;
try$# $$ LANGUAGE plpgsql SECURITY DEFINER;
CREATE FUNCTION
try=# SELECT try_me();
NOTICE: Found: f
NOTICE: Row Count: 1
try_me
--------
(1 row)

Note that FOUND is false, but the ROW_COUNT fetched by GET
DIAGNOSTICS is set to 1. So shouldn't FOUND be true? Or does it just
not work with EXECUTE and need to be documented as such? Or am I just
missing something obvious?

Thanks,

David