I just registered at http://superuser.com.
I got my 100 rep for accociating, and then suddenly a
I clicked the helpful link (mod rights required), and here is my answer, answered by me, which I never answered on superuser.
I did post this answer on stackoverflow, but obviously, that was only after the answer has been migrated, because I wasn't registered on superuser back then.
As far as my permissions let me see, the question was not first migrated to superuser and then migrated back. It originated at superuser and then ended up at stackoverflow.
So I'm really curious, how did my answer end up there? And also look at the comment, it exists on both sites, posted by same user, and the link to the user points to their proper site-specific user page.