BUG #7641: ERROR: must specify relation and object name when function contains DROP TRIGGER

The following bug has been logged on the website:

Bug reference: 7641
Logged by: Sergey
Email address: sergey(at)booksys(dot)com
PostgreSQL version: 9.2.1
Operating system: Windows XP / Ubuntu 10.04 (Lucid)
Description:

Postgres 9.2.1
Reproduced the problem on Windows XP and Ubuntu 10.04

Steps to reproduce:

1. Create a new database:
CREATE DATABASE test;
Connect to the new database.

2. CREATE TABLE test1 (id int);

3.
CREATE OR REPLACE FUNCTION drop_trigger_test() RETURNS void AS $$
BEGIN
DROP TRIGGER IF EXISTS invalid_trigger ON test1;
END; $$ LANGUAGE plpgsql;

4. SELECT drop_trigger_test();
Result:
NOTICE: trigger "invalid_trigger" for table "test1" does not exist,
skipping
CONTEXT: SQL statement "DROP TRIGGER IF EXISTS invalid_trigger ON test1"
PL/pgSQL function drop_trigger_test() line 3 at SQL statement

5. SELECT drop_trigger_test();
Result:
ERROR: must specify relation and object name
CONTEXT: SQL statement "drop trigger if exists invalid_trigger on test2"
PL/pgSQL function drop_trigger_test2() line 3 at SQL statement

For some reason I can run this function without error only once on a fresh
connection. Did not have this problem in 8.4.x and 9.1.6