I'm not sure exactly how long it's been gone, but i just noticed my entire list was erased (except for one or two people) for some reason. Sending friend requests and such seems to work properly though.
Is it possible that they removed you as a friend after you left? You were pretty adamant that you had no intention of coming back.
It's possible that some people might have removed me, but there were alot of people in my friends list who've been inactive for a long time. Among them people who didn't even know me. I doubt they came back just to remove me. I doubt it. A permaban is in essence the same as any other temporary ban (as far as i know). I'm sure it would've been reported already if formerly banned members experienced the same issue. However, I experienced several weird random glitches while in the probation group. This friends list thing might be one as well. It's all i can think of anyway.
In terms of the perma banning question: yes it's the same thing as any other banned user, just with an undefined time period (makes it infinite). While it may seem more obvious that the probation period you were in might have caused this, I have a few doubts. The permission settings are specifically designed to not change or delete any important data, just hide or disable. I know for a fact that there is only one main permission setting that alters friends lists, and it's simply the ability to add friends. Your contact list and current friends would be preserved if this was changed. Given that your profile might have been through quite a few alterations as of recent, I can't say for sure what might have happened... Anything I can give is only guesses.
Well, everything seems to be in order again aside from a few people i may have forgotten to add back. I'll post an update on this if it happens again.