Re Prasanna: I'm coming late to the party and assuming that Tablesaw's comment means the server's solution treated R8C8 as a 5, but actually the puzzle as presented (with a 6) is the only one that's unique. With a 5 there, many other solutions exist. That is a pretty nice puzzle too.
You're right on your assumption(according to Deb). As for the multiple solutions, since the solution is treated as a 5, I assumed that to be correct and forming a valid puzzle, and didn't really check it out. Having looked back, I agree my assumption was wrong, and that only the one with a 6 gives a unique solution.