This is the default behaviour of the javascript object Date. To solve this issue, please override the $.fn.datebox.defaults.parser function to fill with '20' as the prefix while typing only 2 digital number.
$.extend($.fn.datebox.defaults, {
parser: function (s) {
var CDate = $.fn.calendar.defaults.Date;
if ($(this).data('datebox')) {
CDate = $(this).datebox('calendar').calendar('options').Date;
}
if (!s) return new CDate();
var ss = s.split('/');
var m = parseInt(ss[0], 10);
var d = parseInt(ss[1], 10);
var y = parseInt(ss[2], 10);
if (!isNaN(y) && !isNaN(m) && !isNaN(d)) {
if (y < 100) {
y = 2000 + y;
}
return new CDate(y, m - 1, d);
} else {
return new CDate();
}
}
})