can't connect with md5 encrypted pw

hi all

i tried to explain my problem in the following lines. for me it is
necessary to connect my db with the unix user and md5 encryption on my
local machine. i couldn't found a solution. thx for any idea!

my system:
PostgreSQL 8.2.6 on i486-pc-linux-gnu, compiled by GCC cc (GCC) 4.1.3
20070929 (prerelease) (Ubuntu 4.1.2-16ubuntu2)

my problem:
createdb test
psql -U john -d test -W
password:******
psql: FATAL: password authentication failed for user "john"

my pg_hba.conf:
#TYPE DATABASE USER CIDR-ADDRESS METHOD
local all all md5

my roles:
rolname | rolsuper | rolcanlogin | rolpassword
---------+----------+-------------+-------------------------------------
postgres | t | t | md5xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
john | f | t | md5xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

my description:
-john is my unix user
-postgresql server is reloaded
-connecting with my postgres user and md5 works fine
-connecting with "john" and METHOD ident sameuser works although fine
-why can't i connect with my unix user using md5 in pg_hba.conf ?

--
Best regards,

Thomas Schuster