BUG #6712: PostgreSQL 9.2 beta2: alter table drop constraint does not work on inherited master table

The following bug has been logged on the website:

Bug reference: 6712
Logged by: Miroslav Šulc
Email address: miroslav(dot)sulc(at)fordfrog(dot)com
PostgreSQL version: Unsupported/Unknown
Operating system: Gentoo Linux
Description:

here is the test case:

test=# create table test_constraints (id int, val1 varchar, val2 int, unique
(val1, val2));
NOTICE: CREATE TABLE / UNIQUE will create implicit index
"test_constraints_val1_val2_key" for table "test_constraints"
CREATE TABLE
test=# create table test_constraints_inh () inherits (test_constraints);
CREATE TABLE
test=# alter table only test_constraints drop constraint
test_constraints_val1_val2_key;
ERROR: constraint "test_constraints_val1_val2_key" of relation
"test_constraints_inh" does not exist

postgresql tries to drop the constraint even from descendant table though
"only" is specified.