Magic calendar, date doesn't match the day using JS/jQuery

Question

The problem with this calendar that, in the current month the date match with the day, but when you go back for example one month you will find that the date doesn't match the day.

This is the DEMO.

Example August 1, 2013 is a Thursday, but this calendar show me a Friday..

A screenshot showing the problem

Code :

$(document).ready(function () {
    $(".calender").magiCalender();
});

Answer 1

I fixed the problem : DEMO

Code :

if(tMonth < month){
    mod = 5 - mod;
}