I just found a little glitch in the enemy editor. Whenever you edit one enemy, then exit out and select the Trigger enemy, it causes the Trigger enemy's type to be changed to whatever type the last enemy selected is set to.
Enemy Editor Glitch
The problem was that the trigger enemy's type is actually Guy, which doesn't have an entry in the list. I changed it to (None); that won't affect existing 2.50 quests.
Confirmed fixed.