BUG #2261: ILIKE seems to be buggy on koi8 input

The following bug has been logged online:

Bug reference: 2261
Logged by: Evgeny Gridasov
Email address: eugrid(at)fpm(dot)kubsu(dot)ru
PostgreSQL version: 8.1.2
Operating system: Debian Linux
Description: ILIKE seems to be buggy on koi8 input
Details:

my terminal is RU_ru.KOI8-R,
template1's encoding is UTF8.
ILIKE seems to be buggy when comparing russian strings,
while UPPER/LOWER works OK.

template1=# \encoding koi8;

try to get uppercase of some russian letters:
template1=# select upper('');
upper
-------

(1 row)

result is OK!

next, try to compare uppercase and lowercase using
ILIKE:
template1=# select true where '' ilike '';
bool
------
(0 rows)

OOPS! Nothing happened. But why?

try the same but with latin charset letters:

template1=# select true where 'asdf' ilike 'ASDF';
bool
------
t
(1 row)

Try to compare lowercase with lowercase (russian):

template1=# select true where '' ilike '';
bool
------
t
(1 row)

it works.