If an EVENT is created without the DEFINER clause set explicitly or with it set  
to CURRENT_USER, the master and slaves become inconsistent. This issue stems from 
the fact that in both cases, the DEFINER is set to the CURRENT_USER of the current 
thread. On the master, the CURRENT_USER is the mysqld's user, while on the slave,  
the CURRENT_USER is empty for the SQL Thread which is responsible for executing 
the statement.

To fix the problem, we do what follows. If the definer is not set explicitly,  
a DEFINER clause is added when writing the query into binlog; if 'CURRENT_USER' is 
used as the DEFINER, it is replaced with the value of the current user before 
writing to binlog.