ExtJs converts certain valid

I know I previously asked a similar question enter link description here. This is however, slightly different. ExtJs 2.1 is still converting certain invalid dates like 01/00/2012 to 01/01/2012 I was able to create the code below to prevent this from happening, however this creates a 'script error'. Can anyone help me with a solution that does not generate a script error? Here is the code to create the field:

        var d = new Ext.form.DateField({
            el: el.dom,
            id: id,
            format: 'm/d/Y',
            hideTrigger: false,
            allowBlank: true,
            disabled: isDisabled,
            validator: extraDateValidator,
            altFormats: 'm/d/Y|m/j/y|n/d/y|m/j/Y|n/d/Y|m-d-y|m-d-Y|mdy|mdY|d|Y-m-d',
            validateOnBlur: true,
            //validationEvent: false,  //string or boolean
            invalidText: 'Enter date as MM/DD/YYYY',
            menuListeners: Ext.applyIf({
                select: function (m, d) {
                    Ext.form.DateField.prototype.menuListeners.select.apply(this, arguments);
                    this.focus.defer(100, this);
                    onDateSelect(m, d, this);
                }
            })
        });

And here is my validator:

function extraDateValidator(date) {
var dateArray = date.split("/");
if (tempForParseDate) {
    Date.parseDate = tempForParseDate
}
if (dateArray.length == 3 && (dateArray[0] > 12 || dateArray[0]<1 || dateArray[1]<1) ) {
    tempForParseDate = Date.parseDate
    Date.parseDate = "";
    return false;
}
return true;

}

The error I'm getting is: TypeError: Date.parseDate is not a function. As mentioned I am creating it on purpose by these lines in my validator:

 tempForParseDate = Date.parseDate
 Date.parseDate = "";

Stack trace:

initComponent(D="01/00/2012")ext-all.js (line 128)
initComponent()ext-all.js (line 128)
onResize()ext-all.js (line 125)
onResize(A=[Trial] Ext.EventObject {})ext-all.js (line 125)
EventManager(b=[Trial] Ext.EventObject {})ext-all.js (line 13)
getViewWidth(R=keydown charCode=0, keyCode=9)ext-base.js (line 10)

If you really want to re-write Date.parseDate and not get a JS error, then set it to a no-op function, instead of a string.

Date.parseDate = function(){};

Or better, log when that re-written parseDate function is called so you can at least figure out if your code is doing the right thing.

Date.parseDate = function(){
  console.log("Called parseDate with args ", arguments);
};