re: "Could you give us the most recent sequence of events in their activity log?"
Here is the sequence of events:
Aug. 12, approx. 2 AM -- He subscribed himself, via email.
Aug. 12, shortly after (I think within 1 hour) -- I discovered the new member.
Aug. 12, minutes later -- I changed his permissions (*).
Aug. 12, seconds later -- I banned him from the group.
Aug. 12, seconds later -- I verified that he was no longer listed at the top of the Members list.
Aug. 13, 4:45 PM -- He unsubscribed himself, via web.
(*) I routinely lock up their permissions right before banning them. It should not matter, because when they're gone, they're gone (right??), but I do it anyway just in case.
So I think about 38 hours passed between being banned, and him unsubscribing himself.
In case you wonder why I banned him so quickly, I have reasons.