Unregistering command not working, even if typing the players name, is this a bug or intentional?

[HTMLDevelopment]

A player from my server reinstalled his minecraft modpack and cannot log into the server because his password changed, he's a cracked minecraft player, though, so how can i unregister him and is this an intentional feature against cracked players?

[HTMLDevelopment]

nevermind, discovered that the mod makes player names lowcase, so you gotta type them in lowercase for it to work, also better to use the autocomplete feature