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."
Environment
Windows 7 Enterprise (SP1) x64
Intel core i5
CPU @ 2.5 GHz
4.00 GB RAM
Installed Java: 6.0 update 17, 6.0 update 31(x64), 7.0.0(x64)
Working as intended. The kill command only affects you, not any other player.