BUG #7783: lower & upper function incorrect work

The following bug has been logged on the website:

Bug reference: 7783
Logged by: Alexander Shniperson
Email address: alex(dot)shniperson(at)gmail(dot)com
PostgreSQL version: 9.1.7
Operating system: osx lion 10.7.5
Description:

Hi.

I have problem at my project, try to do simple steps:
1) create DataBase with
ENCODING = 'UTF8'
LC_COLLATE = 'C'
LC_CTYPE = 'C'

2) create new table at just created database

CREATE TABLE testtable
(
id serial NOT NULL,
name character varying(50) NOT NULL,
CONSTRAINT testtable_pkey PRIMARY KEY (id )
)

3) insert one simple record with Russian word

INSERT INTO testtable (id, name) VALUES (1, 'Залог');

4) try to select data with upper & lower functions with 'like' operator

select *, lower(name), upper(name) from testtable where lower(name) like
'%залог%'

5) as result you must see nothing, just fields without data

fix it please, thanks.