Triggered Spawners on Trigger Enter

I use both Core GameKit and Master Audio for everything and love it.
  I think there is something I am just missing or I am using it wrong though for Triggered Spawners.  So my rooms are mainly boxes separated by automatic sliding doors that shut once an enemy spawns.  So the player is not crushed by the door or moves quickly back into the previous room (locking themselves out)  I have the Triggers for the Triggered Spawners slightly smaller than the room so you have to venture the whole way in the room.  
  The problem I am having is that if in the middle of combat you back up against a wall and then re-enter the trigger volume before it is done spawning it's 5-7 enemies it will trigger another wave from that spawner.  I never noticed it since I do not run along walls but one of my testers was coming across encounters where like 40 enemies were spawning and I found out this was happening. I use "Disable Event After" and if it finishes the entire wave it is fine but I have the enmies spawn over the course of 30 seconds and it is during that time I can trigger the spawning event multiple times.  

Is there anyway to make it only trigger once on enter? Some setting I haven't understood?

I could make an FSM that "on trigger enter" deactivates the box collider I am using as a trigger but that would possible add like 80 FSMs to any given level and that is a performance concern.