DatePicker incorrect behaviour for defaultDate

I noticed that datepicker does not work properly in calendar mode, and it does not reset ui-state-active after you change months, it looks quite bad. For example if default date is 31st of January, and you clicking on next month 28th of February would be activated automatically.

Example:

<div id="calendar"></div>

<script type="text/javascript">
$('#calendar').datepicker({
	"dateFormat":"yy-mm-dd",
	"defaultDate":"2010-07-31"
});
</script>