I don't know, I felt the correct sign the first time I read it. I also didn't get confused by the cognitive reflection test (in the sense that there is no confusion, the correct way of seeing the problem is all there is). It's really hard to imagine how a person with math training can miss that.

But from what I heard, a sizable portion of math students still manage to get confused by these. Tracing the analogy to cognitive biases, there may be a qualitative difference between a person who just knows about it "in theory" and even done a lot of reading on the topic ("typical" math student), and a person who thought about the techniques at every opportunity for a number of years.