BUG #14209: Rules don't validate duplicated keys

The following bug has been logged on the website:

Bug reference: 14209
Logged by: Abdel Perez
Email address: juniorperezpy(at)gmail(dot)com
PostgreSQL version: 9.5.1
Operating system: Window 7 Professional
Description:

I've a list with duplicates values I use like pk and I create a rule like
this:

CREATE OR REPLACE RULE db_table_ignore_duplicate_inserts AS
ON INSERT TO products
WHERE (EXISTS ( SELECT 1
FROM products
WHERE products.id = new.id AND btrim(products.description::text) =
btrim(new.description::text))) DO INSTEAD NOTHING;

when I insert individually the rule works and its says me he ignores the
duplicate row, but when insert this way:

insert into products (id, description) values (1, 'product1'), (1,
'producto1);

he inserts anyway the two rows.

I didn't see in the documentation that the rule must ignore this cases.