Strange bug with last versione of Jquery!

Strange bug with last versione of Jquery!

Hi, i've this html code:

  1.          <span id="disponibilita">Disponibilità
  2.                 <input type="checkbox" id="illimitata" name="illimitata"/>
  3.                 <span id="scrittaIllimi">illimitata</span>
  4.                 <span id="oppure"> oppure <input type="number" size="2" id="numeroDisponibili"/> pezzi </span>
  5.           </span>

and this JS script

  1. $('#illimitata').change(function()
  2.                         {
  3.                            alert('clicked') //<---This is always showed
  4.                             if ($('#illimitata').attr('checked'))
  5.                             {$('#oppure').hide()} //<---But this don't works with latest version of JQ
  6.                             else
  7.                             {$('#oppure').show()}
  8.                         })

But i'm unable to switch from hide to show using the last version of jquery
  1. <script src="http://code.jquery.com/jquery-1.9.1.min.js"></script>

While with this works
  1. <script src="http://code.jquery.com/jquery-1.8.1.min.js"></script>


Why did happen this?