errors in forum display

after migrating to drupal 4.6 RC i can't no longer see forum content. Posts can be seen correctly if selected via tracker, but choosing the forum page I obtain the following errors:

user error: Illegal mix of collations (utf8_unicode_ci,IMPLICIT) and (latin1_swedish_ci,IMPLICIT) for operation 'if'
query: SELECT n.nid, l.last_comment_timestamp, IF(l.last_comment_uid, cu.name, l.last_comment_name) as last_comment_name, l.last_comment_uid FROM node n, node_comment_statistics l /*! USE INDEX (node_comment_timestamp) */, users cu, term_node r WHERE  n.nid = r.nid AND r.tid = 6 AND n.status = 1 AND n.type = 'forum' AND l.last_comment_uid = cu.uid AND n.nid = l.nid ORDER BY l.last_comment_timestamp DESC LIMIT 0, 1 in /web/htdocs/www.drupalitalia.org/home/drupal-cvs/includes/database.mysql.inc on line 66.

user error: Illegal mix of collations (utf8_unicode_ci,IMPLICIT) and (latin1_swedish_ci,IMPLICIT) for operation 'if'
query: SELECT n.nid, l.last_comment_timestamp, IF(l.last_comment_uid, cu.name, l.last_comment_name) as last_comment_name, l.last_comment_uid FROM node n, node_comment_statistics l /*! USE INDEX (node_comment_timestamp) */, users cu, term_node r WHERE  n.nid = r.nid AND r.tid = 4 AND n.status = 1 AND n.type = 'forum' AND l.last_comment_uid = cu.uid AND n.nid = l.nid ORDER BY l.last_comment_timestamp DESC LIMIT 0, 1 in /web/htdocs/www.drupalitalia.org/home/drupal-cvs/includes/database.mysql.inc on line 66.

user error: Illegal mix of collations (utf8_unicode_ci,IMPLICIT) and (latin1_swedish_ci,IMPLICIT) for operation 'if'
query: SELECT n.nid, l.last_comment_timestamp, IF(l.last_comment_uid, cu.name, l.last_comment_name) as last_comment_name, l.last_comment_uid FROM node n, node_comment_statistics l /*! USE INDEX (node_comment_timestamp) */, users cu, term_node r WHERE  n.nid = r.nid AND r.tid = 11 AND n.status = 1 AND n.type = 'forum' AND l.last_comment_uid = cu.uid AND n.nid = l.nid ORDER BY l.last_comment_timestamp DESC LIMIT 0, 1 in /web/htdocs/www.drupalitalia.org/home/drupal-cvs/includes/database.mysql.inc on line 66.

user error: Illegal mix of collations (utf8_unicode_ci,IMPLICIT) and (latin1_swedish_ci,IMPLICIT) for operation 'if'
query: SELECT n.nid, l.last_comment_timestamp, IF(l.last_comment_uid, cu.name, l.last_comment_name) as last_comment_name, l.last_comment_uid FROM node n, node_comment_statistics l /*! USE INDEX (node_comment_timestamp) */, users cu, term_node r WHERE  n.nid = r.nid AND r.tid = 9 AND n.status = 1 AND n.type = 'forum' AND l.last_comment_uid = cu.uid AND n.nid = l.nid ORDER BY l.last_comment_timestamp DESC LIMIT 0, 1 in /web/htdocs/www.drupalitalia.org/home/drupal-cvs/includes/database.mysql.inc on line 66.

user error: Illegal mix of collations (utf8_unicode_ci,IMPLICIT) and (latin1_swedish_ci,IMPLICIT) for operation 'if'
query: SELECT n.nid, l.last_comment_timestamp, IF(l.last_comment_uid, cu.name, l.last_comment_name) as last_comment_name, l.last_comment_uid FROM node n, node_comment_statistics l /*! USE INDEX (node_comment_timestamp) */, users cu, term_node r WHERE  n.nid = r.nid AND r.tid = 10 AND n.status = 1 AND n.type = 'forum' AND l.last_comment_uid = cu.uid AND n.nid = l.nid ORDER BY l.last_comment_timestamp DESC LIMIT 0, 1 in /web/htdocs/www.drupalitalia.org/home/drupal-cvs/includes/database.mysql.inc on line 66.

maybe developer was swedish?

error can be seen in my test installation here:

http://www.drupalitalia.org/drupal-cvs/?q=forum