This is bewildering and concerning. I absolutely applaud the authors for releasing their code and asking the public to have a look, as well as raising the alarm

This is bewildering and concerning. I absolutely applaud the authors for releasing their code and asking the public to have a look, as well as raising the alarm. Given the degree of due diligence they've performed, it seems too much to hope that there's just some really nightmarish data leakage occurring; but even if that were the case, the difficulty of identifying its origin or even determining the true characteristics of what the models are doing is extremely problematic regardless of whether this particular instance of bias can be explained.