Pretty straightforward, its what the title says.
Screenshot (courtesy of KronoS, who first noticed something was wrong):
The ping works in that the notification shows up, as well as the sound, but the name is not highlighted.
This was caused by this rather huge change to chat's handling of @replies. Fixed now, thanks for the report.
mention
class to the<span>
element with the username. But it's way too complicated and obfuscated for me to look into that right now :P