Dialog wont reposition position

I'm having a problem with 1.8rc2 dialogs.

The dialog opens and after it opens needs to set itself to the center. this works fine with 1.7 but in 1.8rc2 its opens at the bottom left of the screen. the following code worked fine to reposition itself to center but wont work in 1.8rc2.

$("#ui-dialog-notice").dialog({
	bgiframe: true,
	resizable: false,
	height:140,
	modal: true,
	buttons: {
		'Close': function() {
			$(this).dialog("close");
			}
		},
	close: function(event, ui) {
		$("#ui-dialog-notice").remove();	
	},
	open: function(event, ui) {
		$("#ui-dialog-notice").dialog('option', 'position', 'center');
	}
});