ENTER_BR option doesn't work anymore ?

Hi,

I build up a little plugin wich prevent deleting text if the backspace key
is holding down.
I grab the most part of the code from the keystrokes plugin, here's my code:

CKEDITOR.plugins.add('nobackspace,
{
    init: function(editor)
    {
        var pluginName = 'nobackspace';
    }
});


(function() 
{
        var pressed;

   var onKeyPress = function( event )
   {
      if( event.data.$.keyCode == 8 )
      {
         if(pressed === true)
         event.data.$.preventDefault();
         else
      pressed = true;
     };
   }

   var onKeyUp = function( event )
   {
    if ( event.data.$.keyCode == 8)
        pressed = false;
   }

   CKEDITOR.keystrokeHandler.prototype =
   {
       attach : function( domObject )
       {
     domObject.on( 'keypress', onKeyPress, this);
     domObject.on( 'keyup', onKeyUp, this);
       }
    };

})();

It works fine except now the "ENTER_BR;" option has no
effect anymore.
If I press the enter key, a new paragraphe is still created in the editor.

Can someone please tells me why and how to fix it ?

Thanks.