JQuery.validate () validation even if nothing is entered

I am working with the validate () method in jQuery. According to the documents :

If nothing is entered, all rules are skipped, except when the field has already been marked as invalid.

and the following code:

$("#Form").validate(
{
      errorClass: "dialogerror",
      onfocusout:          function(element)
                         {
                             $(element).valid();
                         },
      onkeyup: false
}); 

However, it gives an error message even if nothing is entered , so I assume the item is flagged as invalid at boot, could this be true? Perhaps the option is set somewhere, and I'm looking in the wrong place.

Any advice is greatly appreciated.