I agree this should be acknowledged.

In this particular case, the workaround is luckily simple:

  case String.fromInt n of
    Just "-1" -> True
    _         -> False

I'm generally fine with language quirks like this, but I understand why others wouldn't be.

A number is not a string, you should not have to convert to strings like this. Evan's response on that issue is very typical - ask a question, get a negative reaction, completely ignore it and years later zero indication of a fix or change.