This bug is effective on a singleplayer world (or multiplayer with LAN). This bug will cause the player who enters the [/kill] command to die, regardless of the target player.
To reproduce:
1) Create a Singleplayer world (Cheats enabled)
2) Enter the [/kill] command with either yourself OR an imaginary player as target. Effect will be your Death no matter what playername you entered, with the message "[playername] fell out of the world. Ouch. That looks like it hurt."

OR

1) Create a Singleplayer world (Cheats Enabled)
2) Open to LAN
3) Invite friends/family to join on your LAN
4) Enter the [/kill] chat command with any in-game player as the target.
Effect will be your death no matter who the target was, with the message "[playername] fell out of the world. Ouch. That looks like it hurt."