When ever you use the command /effect <Player> 8 <1-1,000,000> 255, the player doesn't and as far a i know isn't suppose to jump nor get falling damage, but when ever you get hit while jumping you get a HUGE knock back i noticed this when i was on fire with the effect enabled an i went flying up in the air uncontrollably. To re-enact just set the jump boost affect on 255 for your self and jump while taking damage from something while your in survival mode.