This is still the case today.

Expected: [], instead got: [4,2] for these values:

function isEven(num) {
  return num % 2 === 0;
} 

[ 1, 4, 2, 3, 5, 4, 5, 6, 7 ]

and another one:
Expected: [], instead got: [3,5] for these values

function isOdd(num) {
  return num % 2 !== 0;
} 
[ 2, 1, 2, 4, 3, 5, 4, 6, 7, 8, 9, 0 ]

If the submit function fails to send data to the server, the button remains disabled and I am unable to resubmit easily.

Great product though!!