When you select to perform a /whois by clicking on a player name, in a PM, it appends the colon to the end of the player name and cites them as an unknown player. It only affects the name of the person who you are in a PM with. You can click to /whois yourself in the same PM. I am on KoLmafia v15.1 r10940, on Mac OS 10.7.3. I reproduced this by opening several other PMs and trying the /whois on the other player in them. This was the KoLmafia Chat, not the chat to the right of the main pane.