"minecraft.killed:minecraft.player" doesn't increase when killing players

The Bug:

"minecraft.killed:minecraft.player" doesn't increase when killing players.

Steps to Reproduce:

1. Create a scoreboard objective for tracking when you kill a player and set it to display on the sidebar by using the commands provided below. 

   /scoreboard objectives add KillPlayer minecraft.killed:minecraft.player

   /scoreboard objectives setdisplay sidebar KillPlayer

2. Kill a player.
3. Take note as to whether or not "minecraft.killed:minecraft.player" increases when killing players.

Observed Behavior:

"minecraft.killed:minecraft.player" doesn't increase when killing players.

Expected Behavior:

"minecraft.killed:minecraft.player" would increase when killing players.