Killing an End Crystal with /kill damages the Ender Dragon

The bug

Using commands to kill end crystals damages the ender dragon.

How to reproduce

1. Make sure you have cheats enabled
2. Turn off mob griefing:

   /gamerule mobGriefing false
   

3. Summon an end crystal and an ender dragon
4. When the dragon's using the healing beam, run:

   /kill @e[type=end_crystal]
   

   → The crystal will vanish but the ender dragon will lose health