I don't think it's strange at all. Bernstein is the more logical spelling, based on how it's pronounced, so absent any other signaling I just imagined it that way. Add to that the fact that it's usually stylized in cursive, in which it's harder to make out the letters, it's not surprising people get it wrong. After apartheid sort of faded from memory (not completely but I mean as a current event), Mandela was less important, and so it was easy to forget he was alive. I can't keep track of every old guy in the world.