What happening:
Endermites are dissapearing

What actually happening:
they loses their heads after /kill @e[type=Endermite]

Steps to prove the glitch/bugs
1. Summon many endermans in 1 room with rapid clock
2. Kill them with /kill @e[type=Enderman] with /kill @e[type=Endermite] attached to a rapid clock
3. and then look at the room, the endermite loses their heads