Snowballs, Enderpearls and Eggs do not knockback players in multiplayer

In a LAN world when I throw a Snowball/Egg or use a Fishing rod, it goes right through the target player, without pushing them, or latching on in case of the rod. I do have Optifine installed, the LAN host had no mods.

What I expected to happen was: For the Egg/Snowball to hit them back, and the rod to hook them.

What actually happened was: None of the items affected them at all.

Steps to Reproduce:
1. Start a LAN world.
2. Equip one of the items, and throw it at a player.
3. Watch as it goes through them, causing no effects.

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Code analysis by Marcono1234 in this comment