The basic results are interesting, but what really surprised me is that asking them to double-check didn't work. Falling for an "optical illusion" is one thing, but being unable to see the truth once you know the illusion there is much worse.
You can test this claim by asking it to double-check itself when you think it is correct. If you always stop when it gets it right you're risking Clever-Hans-ing yourself: https://en.wikipedia.org/wiki/Clever_Hans (And be sure to do it a couple of times. In situations of sufficient confidence it isn't easy to talk it out of a claim, but it's those borderline ones you want to worry about.)