Fireballs curve after being hit by slimeblocks

Fireballs tend to move in a parabolic (x^2) trajectory instead of a straight line ( x ) after being punched by a slime block.

Steps to reproduce:

1. Load the attached structure file mc_108772.nbt
2. Trigger the button
   -> The fireball will only curve after being hit by the slimeblocks and fly straight up eventually again, instead of flying in a straight line after being hit by the slimeblocks