my.cnf includedir not working as expected

The last lines in /etc/mysql/my.cnf (Gutsy) says
#
# * IMPORTANT: Additional settings that can override those from this file!
#
!includedir /etc/mysql/conf.d/

I want MySQL running with UTF-8, hence:

1/
# printf "[mysqld]\ncharacter-set-server=utf8\ndefault-character-set=utf8\n" > /etc/mysql/conf.d/huhu

2/
# /etc/init.d/mysql restart
 * Stopping MySQL database server mysqld
   ...done.
 * Starting MySQL database server mysqld
   ...done.
 * Checking for corrupt, not cleanly closed and upgrade needing tables.

3/
# mysql -uroot -Bse 'SHOW VARIABLES LIKE "char%"'
character_set_client latin1
character_set_connection latin1
character_set_database latin1
character_set_filesystem binary
character_set_results latin1
character_set_server latin1
character_set_system utf8
character_sets_dir /usr/share/mysql/charsets/

4/
Didn't work, character_set_server should've been utf8.

What works is the following:
1/
Edit /etc/mysql/my.cnf and add this right below [mysqld]
character-set-server = utf8
default-character-set = utf8

2/
# /etc/init.d/mysql restart
 * Stopping MySQL database server mysqld
   ...done.
 * Starting MySQL database server mysqld
   ...done.
 * Checking for corrupt, not cleanly closed and upgrade needing tables.

3/
# mysql -uroot -Bse 'SHOW VARIABLES LIKE "char%"'
character_set_client latin1
character_set_connection latin1
character_set_database utf8
character_set_filesystem binary
character_set_results latin1
character_set_server utf8
character_set_system utf8
character_sets_dir /usr/share/mysql/charsets/

More info:
# dpkg -l |grep mysql
ii libdbd-mysql-perl 4.004-2 A Perl5 database interface to the MySQL data
ii libmysqlclient15off 5.0.45-1ubuntu2 MySQL database client library
ii mysql-client-5.0 5.0.45-1ubuntu2 MySQL database client binaries
ii mysql-common 5.0.45-1ubuntu2 MySQL database common files
ii mysql-server-5.0 5.0.45-1ubuntu2 MySQL database server binaries
ii php5-mysql 5.2.3-1ubuntu4 MySQL module for php5