Clearly, Yoda has 900 years of experience dealing with datetime bugs.

If you mean Joda time, then "xxxx" is also affected (which is correct behavior):

  public static void main(String[] args) {
    long now = System.currentTimeMillis();
    System.out.println("YYYY: " + DateTimeFormat.forPattern("YYYY").print(now));
    System.out.println("yyyy: " + DateTimeFormat.forPattern("yyyy").print(now));
    System.out.println("xxxx: " + DateTimeFormat.forPattern("xxxx").print(now));	
  }

prints

  YYYY: 2014
  yyyy: 2014
  xxxx: 2015

Nobody will use xxxx by accident, so it's not 'affected' by any problem/confusion, it's just there doing what the developer intended.

Y and y are only different for BC dates in the Gregorian calendar, so using the incorrect one generally isn't going to cause problems.