"___ is not in your guild" problem

So I recently made a bank toon, got people to sign my charter in exchange for gold and having no other responsibility towards the charter or guild as they would be kicked out.
However after forming it, and kicking everyone out, my guild info shows one other person in the guild. However I cannot kick them!
It says "[Person] is not in your guild."
Well it clearly shows them in the guild rankings still. I did a re-log, and they're still there. This makes no sense. They hadn't deleted their character as I can put them on the friends list.
Has anyone else ever had this problem? I'm worried about a security risk although they do not have any powers in terms of the guild bank.

Thanks.