Fireballs disappear in Water and appear when you delete the waterspot (you can see smoke and waterdrip particles in the picture) 
No - they dont disapear - they only hide. if u punch them they explode.
How to test in your own World:
First summon a Fireball:
/summon Fireball ~ ~ ~
Set Water above the Fireball
Punch the water
oh - and sorry for the creepy English, iam German 
Hope this wasnt the 1000 duplicate,
froggy 
- duplicates
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MC-9553 Wrong rendering order of particles, hitboxes, clouds, transparent blocks, breaking animations and various other transparent textures
- Resolved