I have noticed that avatars from banned members are getting removed from the filesystem. At first I was thinking that they were getting removed (S, M and L versions) at the moment when the ban was executed (be it from a warning action or by using the spam cleaner) however I have noticed that the removal from the filesystem happens some hours later but unfortunately I'm not exactly sure how many hours later or if it is done by a cron job.
At first I was thinking that the culprit was the add-on Special Avatar for Banned Members by @Chris D however he has already told me that his add-on does nothing to the avatar files.
So I'm not sure what could be causing this. What should I check?