Description:
According to WL#1218: 
-- The trigger name must be a valid identifier (same rules  
as for  other object names), and must be unique within the  
schema/database.  But I am able to create two triggers 
that have the same name; this should be disallowed. 

How to repeat:
mysql> create table t2 (col1 int, col2 int) engine=memory; 
Query OK, 0 rows affected (0.01 sec) 
 
mysql> create table t3 (col1 int, col2 int) engine=memory; 
Query OK, 0 rows affected (0.01 sec) 
 
mysql> create trigger t2_bi_1 before insert on t2 for each row begin end; 
Query OK, 0 rows affected (0.00 sec) 
 
mysql> create trigger t2_bi_1 before insert on t3 for each row begin end; 
Query OK, 0 rows affected (0.00 sec) 
-- Note that the trigger name is the same as the name 
of the first trigger created. This statement should be 
rejected with SQLSTATE HY000 trigger already exists

See Bug#5892

Fixed in 5.0.10

Documented in 5.0.10 changelog.