private void nessEndings() {
    if (endsIn('n', 'e', 's', 's')) { /*
                                       * this is a very productive endings, so
                                       * just accept it
                                       */
      word.setLength(j + 1);
      k = j;
      if (word.charAt(j) == 'i') word.setCharAt(j, 'y');
      lookup();
    }
    return;
  }
*
YCS: this was the one place where lookup was not followed by return.
So restructure it. if ((j>0)&&(lookup(word.toString())) &&
!((word.charAt(j) == 's') && (word.charAt(j-1) == 's'))) return;
***
linguistics/src/main/java/com/yahoo/language/simple/kstem/KStemmer.java