Hi,
When usin Stdin.readByte it incorrectly read bytes depending on the value of the previously byte read.
If you look at the code:

static readByte() {
  return read_ {
    // Peel off the first byte.
    var byte = __buffered.bytes[0] // This operates on bytes
    __buffered = __buffered[1..-1] // This operates on UTF8 strings
    return byte
  }
}

Meaning that for every byte values > 127 the whole utf8 character is skipped instead of a single byte.