$.contains() returning 16/0 instead of true/false?

$.contains() returning 16/0 instead of true/false?

is this a bug or am i doing something wrong?
  1.     <div id="A">
            <span id="B"></span>
        </div>
        <span id="C"></span>




  1. console.log($.contains($("#A")[0], $("#B")[0]));        // logs 16
  2. console.log($.contains($("#A")[0], $("#C")[0]));        // logs 0

Leon