Lost sync in MySQL master-master replication

When I set-up a Master-Master replication between 4 servers I usually lose the synchronization between the tables across the servers!

I use this to do the replication:

mysql> slave stop; 
CHANGE MASTER TO MASTER_HOST = '3.3.3.3', MASTER_USER = 'replicator', MASTER_PASSWORD = 'password', MASTER_LOG_FILE = 'mysql-bin.000001', MASTER_LOG_POS = 107; 

slave start;