BUG #5010: perl iconv function returns ? character

The following bug has been logged online:

Bug reference: 5010
Logged by: Lampa
Email address: lampacz(at)gmail(dot)com
PostgreSQL version: 8.4.0
Operating system: Debian testing/unstable
Description: perl iconv function returns ? character
Details:

See the difference (example is the best explanation):

psql -U postgres -p 5433
psql (8.4.0, server 8.3.7)
WARNING: psql version 8.4, server version 8.3.
Some psql features might not work.
Type "help" for help.

postgres=# select my_ascii2('Bockaničová');
my_ascii2
-------------
Bockanicova
(1 row)

psql -U postgres -p 5432
psql (8.4.0)
Type "help" for help.

postgres=# select my_ascii2('Bockaničová');
my_ascii2
-------------
Bockani?ov?
(1 row)

function my_ascii2 is defined:
CREATE FUNCTION my_ascii2(text) RETURNS text AS $$ use strict; use
Text::Iconv; my $conv = Text::Iconv->new("UTF8", "ASCII//TRANSLIT"); return
$conv->convert($_[0]); $$ LANGUAGE plperlu;

8.3.x version works perfectly, 8.4.0 problem

in more complicated queries (joins, conditions) after my_ascii2 function
query are returned incorect count of rows