Do you have a parallel event that is running?
Do you have some sort of tirgger that is not part of Blizz-ABS that you put in to run when an enemy is beaten?
Do you play a sound when an enemy is beaten?
Does this only happen with certain skills, if so, check to see if they run a common event.
Do you have them play a long death animation?
Does that enemy have Leader or Call for Help on?
Does an event run when the enemy is defeated? (Do you have it set to do something when beaten?)
List of all scripts?