Não tenho certeza se isso é exatamente um bug ou apenas um comportamento que não compreendo totalmente, mas parece que citar alguém em uma postagem salva o avatar dessa pessoa naquele momento específico junto com a citação. Como aqui:
I suppose its because the posts are baked with the URL at the time. Do you want a fix for this, or is it too potentially resource intensive to trigger a rebake each time someone changes their avatar?
Changing the avatar already triggers a rebake of posts containing quotes, but it’s currently quite resource intensive to find and rebake all posts. So, it’s possible that some of them won’t be updated. Post revisions aren’t updated at all.
I have plans to fix all of this when I’m working on improvements for user renaming/anonymizing in one of the next releases. It will require a new table that keeps track of all the places where a user is quoted, mentioned, oneboxed, and what not.
If you want to work on this, please keep in mind that rebaking just to update the avatar isn’t needed. I’d suggest reusing code from UpdatUsername. It’s a lot faster.
Isso acontece after_save, mas usa will_save_change, então tenho certeza de que nunca é acionado. Parece que funcionava antes, mas este commit em 2017 (presumo que por engano) mudou de _changed para will_save_change.