The text ".pin" or ".unpin" (based on starring) is appended to the
title attribute of chat flag links.
Wow, that one has gone unnoticed for a while. I was curious; through the magic of source control, I found a changeset from September 20th, 2010 (!), that turned
(Back then, it was still possible to unflag a message, that's why
Anyway, long story short: Fixed.