Mysql get to max connections when creating segments

Hi everyone!

I'm using piwik a lot but I have one problem when creating segments.
When I try to create a new one, I select a variable to add, and it starts to "think". After that, it breaks.

What I've found is the following:
Piwik starts to make again and again the same query with different idvisitors:

SELECT  	idvisitor,
							visit_last_action_time,
							visit_first_action_time,
							idvisit,
							visit_exit_idaction_url,
							visit_exit_idaction_name,
							visitor_returning,
							visitor_days_since_first,
							visitor_days_since_order,
							location_country,
							location_region,
							location_city,
							location_latitude,
							location_longitude,
							referer_name,
							referer_keyword,
							referer_type,
							visitor_count_visits,
							visit_goal_buyer
							 
		
				FROM piwikito_log_visit
				WHERE visit_last_action_time >= '2013-08-23 08:43:05' AND visit_last_action_time <= '2013-08-23 09:43:05' AND idsite = '9' AND idvisitor = '�?�=?��'
				ORDER BY visit_last_action_time DESC
				LIMIT 1

The idvisitor is as it seems, with a strange encoding.

Then, the mysql get to the top of 1000 connections and it breaks.

The machine has the following:
Nginx
php5-fpm
mysql5
24GB RAM
2GB maximum per each php proccess

I hope you can help me with this.
Thank yo so much!