MySQL - Enabling Scheduled Event on Master and Slave Simultaneously
The only way I have found to do this so far is by using: 

On the Master B:

SET SQL_LOG_BIN=0;
ALTER DEFINER=user@localhost EVENT e_test ENABLE;
SET SQL_LOG_BIN=1;


This works, but as soon as I alter the Event on Master A, Master B goes back to Slaveside_disabled and I have to repeat this process. So not perfect by any means, as it relies on us remembering to do this for each event, if we Alter them.