https://sourceforge.net/tracker/?func=detail&aid=3184863&group_id=152762&atid=785191

In the following case, when we open combobox/datebox and scroll down the browser (using mouse wheel, not the browser scroll bar), the popup is kept open and will not follow the combobox/datebox.

Test case:

<hbox width="100%" height="2000px">
<vbox>
Combobox:
<combobox>
<comboitem label="Simple and Rich" />
<comboitem label="Cool!" />
<comboitem label="Thumbs Up!" />
</combobox>
<datebox />
</vbox>
</hbox>

See forum thread:
http://www.zkoss.org/forum/listComment/15282