Steps to Reproduce

Run fiddle:
http://zkfiddle.org/sample/36klec2/2-datebox-popup-visible-false-on-other-popup-close

Click on button to open main popup
Click on datebox button to open datebox popup
Click outside of the main popup to close both popup at the same time

Click on the button to open the main popup
Click on the datebox button to open the datebox popup

Current Result

The datebox popup is open (added to dom tree) but has the visible:false; style rule.
It is opened, but not visible.

Expected Result

The datebox popup should be visible

Debug Info

Main popup closing afterCloseAnima_ calls main popup setVisible(false)
https://github.com/zkoss/zk/blob/d41c1c2afaa24dc783d30c410dd0ba120d306fa3/zul/src/archive/web/js/zul/wgt/Popup.js#L285

main popup setVisible(false) flags all other floating popups as visible:false
https://github.com/zkoss/zk/blob/d41c1c2afaa24dc783d30c410dd0ba120d306fa3/zk/src/archive/web/js/zk/widget.js#L1962

Root Cause

Visible:false is not reverted on datebox when becoming visible.

Workaround

Tested on ZK 8.0.1.1 and ZK 8.0.5

	<script><![CDATA[
	zk.afterLoad('zul.db', function() {
		var xDatebox = {};
		zk.override(zul.db.Datebox.prototype, xDatebox ,{
			setOpen : function() {
				this.$n('pp').style.visibility = '';
				var result = xDatebox.setOpen.apply(this, arguments);
				return result;
			}
		});//zk.override
	});//zk.afterLoad
	]]></script>