maxDate Firefox 3.5.2 issue - calendar locked

The following code should set maxDate of '#pea_date_ret' to the date one month after the date selected at '#pea_date'.

It works fine in IE6 and Opera 9.64, but not in Firefox 3.5.2. In Firefox '#pea_date_ret' is locked at current month (navigation is not available).

	    $('#pea_date').datepicker({
	       onSelect: function(text, inst) { 
		    var max_date=new Date(parseInt(inst.currentYear), parseInt(inst.currentMonth)+1, parseInt(inst.currentDay));
		    $('#pea_date_ret').datepicker('change', {
			defaultDate: $('#pea_date').datepicker('getDate'),
			maxDate: max_date
		    });
		}
	    });