I think this is recently introduced, though it's possible I just haven't noticed until now. But when I open the little dropdown window for my PMs, all of the avatars are the avatar of the last person who sent a PM in any of my conversations. So if it was me, all of them show my Klackon. If it was instead, say, warban, you get the bouncing pony. Which frankly, is kind of obnoxious, seeing 5 of those.
Herbert Hoover got 40% of the vote in 1932. Friendly reminder.