BUG #4579: to_char & utf8

The following bug has been logged online:

Bug reference:      4579
Logged by:          Anton
Email address:      pyo@mail.ru
PostgreSQL version: 8.2 & 8.3
Operating system:   Windows XP
Description:        to_char & utf8
Details:

Hi!

I have DB with UTF8 character set. When I connect to it any client with
client_encoding WIN-1251 and try execute query like:
  select to_char(field, 'FM999G999G999G999') from table;
I get an error:
 invalid byte sequence for encoding "UTF8": 0xa0
HINT: This error can also happen if the byte sequence does not match the
encoding expected by the server, which is controlled by "client_encoding".

Thanks.