When you reel in items with a fishing rod they sometimes do not move smoothly but instead suddenly "jump" or "teleport" to your position.
- Stand diagonally about 3 blocks above an item
- Cast your fishing rod and reel the item in
→ You should see that the item does not smoothly move to you but instead suddenly appears below you
Based on 1.11.2 decompiled using MCP 9.35 rc1
It looks like the check to set the field net.minecraft.entity.Entity.isAirBorne to true in the method net.minecraft.entity.item.EntityItem.onUpdate() is causing this. This won't notice the motion difference because it did not happen during the onUpdate call.