The study is about people confused about something not worthy of further study. At first glance it might look like a study of the thing not worthy of further study itself.
Ah. I see. I don't think that was what was going on here. Wedrifid seemed to find it frivolous because he considered it trivially obvious that the two types of mistakes would occur together. I don't think for example wedrified necessarily consider it frivolous if someone did study which looked for a correlation between not understanding/accepting .999...=1 and say performance at dual-n back or some other task that is not as obviously related to mathematical ability.
I'm mostly asking this open question to those among us who are well-versed in developmental psychology (I'm mostly thinking of children) . Although, failing the actual scientific research on the topic, I guess some testable hypotheses would be great too.