I am curious. Today I wanted to add a message to my signature. My long-standing signature had HTML tags instead of BBcode tags. The additional message had only BBcode. When I saved my profile, I noticed that my long-standing avatar of Jade Feng was replaced with the new "default" avatar image. I panicked a bit, tried to retrieve my old avatar from Google cache, etc. Then I remembered that I had saved the file somewhere on my hard disk.
I just re-uploaded my avatar to my profile, posted in a few places, and all was back to normal. Almost. I notice that now my avatar is in an oval, whereas before it was in a circle. I also have noticed that other avatars are in a circle the same size as mine was before my profile update, and that the "default" avatar is in an even bigger circle. (See attached image.)
It's not a huge thing, but I'm just curious how come things are like this now.