/whonick doesn't deal with duplicate nicks.

[rdebath]

/whonick only shows the first player with a particular nick and complains about multiple players if you use a substring.

> /who
There are 3 players online.
:SuperOPs: red-green-blue (main)
:Anarchists: guesty (main)
:Guests: guesty (main)
> /whonick guest
2 online player nicks match "guest":
guesty, guesty
> /whonick guesty
The player nicknamed guesty is named test+
>