When you are spectating in some mobs (creepers, enderman, spiders) you will see a shader. But when you execute the /kill command, you will keep the shader, although you aren't in the mob. The shader should go away if you aren't in the creeper anymore, but I kept the shader.

How to reproduce:
Summon/find a creeper.
Go into spectator mode.
Click on the creeper.
Press /kill .
You will keep the shader.