Enderman is immune at Firework rocket's explosive damage

Put the summary of the bug you're having here

: First, I'm sorry for my proficiency in English.. Im Korean user.

enderman IS IMMUNE at firework rocket explosion damage.

What I expected to happen was...:
Describe what you thought should happen here

: I was playing multiplayer surver. With blazeandCave's Advancements Pack. And I wanted to achieve "Killing every mob with TNT" achievement in mod pack. And I found that shooting mobs with crossbow loaded with firswork rocket (Of course that I made it with 7 firework stars) counts as killed with TNT. 

So I started to make a lot of firework rocket with 7 stars, and killing every mobs with this.

What I expected was killing enderman with this. Because enderman CAN dodge arrow, but they can't dodge TNT explosion damage.

What actually happened was...:
Describe what happened here

: First, in Nether I found enderman and shoot firework rocket to him. But he just tp to somewhere. So I thought that he just ran away. 

And the second meeting with enderman, I tried he gets on the boat to make killing enderman easier.

Than I found Enderman is immune at explosion damage. 

And I reproduce is again at single play world. And made the same result.

I checked that enderman is the only mob that dodge the damage of firework explosion.

Steps to Reproduce:

1.  Selecting single play world or multiplayer world have nothing to do with this.

2. Make a firework rocket with one or more firework star. I checked that dyes and patterns don't matter at this issue.

3.  Load it into the crossbow. I checked that the enchanments are unaffected at all.

4. Shoot at enderman and check they're immune at this damage. I checked that boat and diminsion are not important.