Incorrectly typed /kill command (like /kill @e[Type=Creeper]) should render in an error, rather than kill EVERYTHING, including all your item frames and armor stands.

It is filed as a suggestion http://www.reddit.com/r/minecraftsuggestions/comments/31urag/kill_with_a_typo_should_not_kill_everything/ as it should – but I actually consider it a bug, even though you might not.