Popup is not closing when you click in the below part of the page

The default behavior of the popups allows to close them when the user clicks on some part of the page except popup element.

We noticed that, popups are not closed when we click in the below of the browser's page. The same problem that we have in out application occurs in the popup's demo in the official ZK's page:
https://www.zkoss.org/zkdemo/popup/pop-ups

More information in attachment.